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This revised edition has been very largely rewritten. The 
emphasis which was laid on motor processes in the volume 
when it appeared in 1907 has been iqpre than justified by 
recent developments of " behaviorism " in psychology. The 
present edition goes further than did the first in working out 
the doctrines of functional psychology, especially in so far as 
these use motor processes in explaining mental organization. 

The doctrine of attitudes which was presented in the 
first edition has been much expanded. 

The applications of psychology have been elaborated, 
especially through a new chapter on mental hygiene. 

The view with regard to the importance of consciousness 
in evolution which was set forth in my paper before the Amer- 
ican Psychological Association in 1909 has been adopted as 
a guiding principle in this volume. In keeping with this 
view, the chapter on volition has been wholly rewritten, and 
several earlier sections have been laigely worked over. 

Perhaps the simplest method of economizing the time 
of those who are interested merely in the new parts will 
be to enumerate the chapters which are not greatly modi- 
fied. These are Chapters I, II, III, V, VIII, IX, X, XI, 
XIV, and XVII. The remainder of the volume includes 
liberal revisions. Chapters IV, VI, VII, XII, XV, and 
XVI are new or very largely so. The book has been freed 
so far as possible from technical controversial discussions, 
with the result that some chapters, notably Chapter XIII, 
have been reduced. 


Many new obligations have accumulated since the first 
edition appeared. Those who have used the book in 
class or have read it in individual study have in many 
instances sent to the author helpful criticisms. All of 
these have been kept in mind in the revision and are 

here gratefully acknowledged. 

C H. J. 


There is very general agreement as to the main topics 
which must be treated in a textbook on psychology. There 
is, however, no accepted method of approaching these 
topics, and, as a result, questions of emphasis and propor- 
tion are always matters of individual judgment. It is, 
accordingly, not out of place for one to attempt in his 
preface to anticipate the criticism of those who take up 
the book," by offering a general statement of the princi- 
ples which have guided him in his particular form of 
treatment. This book aims to develop a functional view 
of mental life. Indeed, I am quite unable to accept the 
contentions or sympathize with the views of the defenders 
of a structural or purely analytical psychology. In the 
second place, I have aimed to adopt the genetic method 
of treatment. It may be well to remark that the term 
" genetic " is used here in its broad sense to cover all that 
relates to general evolution or individual development. In 
the third place, I have attempted to give to the psycho- 
logical conditions of mental life a more conspicuous place 
than has been given by recent writers of general textbooks 
on psychology. In doing this I have aimed to so coordi- 
nate the material as to escape the criticism of producing 
a loose mixture of physiology and introspective description. 
In the fourth place, I have aimed to make as clear as 
possible the significance of ideation as a unique and final 
stage of evolution. The continuity running through the 
evolution of the sensory and motor functions in all grades 
of animal life is not, I believe, the most significant fact for 
psychology. The clear recognition of this continuity which 


the student reaches through studies of sensation and habit, 
and even perception, is the firmest possible foundation on 
which to base an intelligent estimate of the significance 
of human ideational processes. The clear comprehension 
of the dominant importance of ideational processes in man's 
life is at once the chief outcome of our study and the com- 
plete justification for a science of psychology, distinct from 
all of the other special disciplines which deal with life and 
its variations. The purpose of this book may therefore be 
stated in terms which mark as sharp a contrast as possible 
with much that has been said and written of late regarding 
the advantages of a biological point of view in the study 
of consciousness. This work is intended to develop a 
point of view which shall include all that is given in the 
biological doctrine of adaptation, while at the same time it 
passes beyond the biological doctrine to a more elaborate 
principle of indirect ideational adaptation. 

In the preparation of this book I am under double obli- 
gation to A. C. Armstrong. As my first teacher in psy- 
chology, he has by his broad sympathies and critical insight 
influenced all of my work. Furthermore, he has given me 
the benefit of his judgment in regard to all parts of this 
book while it was in preparation. Two others I may men- 
tion as teachers to whom I am largely indebted. The 
direct influence of Wilhelm Wundt will be seen at many 
points in this book. As the leader in the great advances 
in modern psychology, especially in the adoption of experi- 
mental methods, and as the most systematic writer in this 
field, he has left his impression on all who have worked 
in the Leipzig laboratory to an extent which makes such 
a book as this in a very large sense of the word an expres- 
sion of his teaching. Finally, I am indebted to William 
James. I have received instruction from him only through 
his writings, but take this opportunity of acknowledging his 
unquestioned primacy in American psychological thought 


and the influence of his genius in turning the attention of 
all students to the functional explanations of mental life 
which it is one of the aims of this book to diffuse. 

My colleagues, Dr. R. P. Angier and Dr. E. H. Cameron, 
read the manuscript and gave me many valuable sugges- 
tions which have been incorporated into the text. Mr. C. II. 
Smith assisted me in the preparation of the figures. 





Psychology a study of conscious processes. The motive oi wonder. 
Discovery ot individual differences as motive. Diilerences between 
experience and physical fails. Place ol consciousness in evolution. 
The first method ot psychology. Nervous piocesses as conditions of 
consciousness. Studies of heha\ n>r. Overemphasis ot slower forms 
of mental activity tin ough introspection. Kxpcnmenl in ps)chology. 
Explanation at variance with meie obseivation. Subdivisions of 
psychology. Summary and definition of psychology. Definitions of 
certain gencial psychological terms. 


The introspective approach. Indirect method of approach to psy- 
chological iacts. Chaiactenstics of umcellulai animals. Simplest 
types of behavior. Consciousness no more complex than behavior. 
Uehavior more limited than sensitivity. Specialisation of cell struc- 
tures and functions in higher animals Spcciah/ed neivous pi ocesses. 
Nervous processes of three distinct type's IJchavior varied and much 
more complex Progressive evolution in both stiuctuie and behavior. 
Centrali/ed nervous system. Cooulinating center of the body. Com- 
plex paths within the nervous system. Kxpencnec comparable to 
the* lower forms of human experience. Differentiation of vertcbiate 
central nervous system Two types of higher renters : first, higher 
sensory centers; second, indirect centers Large indirect centeis 
characteristic of highest animals. Traces of past impressions also 
present. Meaning of evolution of complex organisms. Innrr organi- 
zation essential to highest foims of personal behavior. Characteristics 
of behavior of higher animals. 


External plan like that of all vertebrates. General plan of the minute 
nervous structure as related to consciousness. The nerve cell and its 
parts. Complexity of structure related to forms of action. Synapses 
as paths of organization. Paths m spinal cord. Reflex tracts. Trans- 
mission to higher centers. All nervous organs in part independent 




centers. Cerebellum. ( 'crchrtim and its systems of fibers. Structure 
of cerebrum as indicating way in which impulses are organized. Cere- 
bral cortex complex. Localization of functions. Stimulation the first 
method of discovering cerebral localization Extirpation and com- 
parison of pathological cases. Krnbryological methods. Association 
areas. Significance of the central position of the general motor area. 
Speech centers. IJroca's convolution an association center. Phre- 
nology not in accord with clearly known facts. Frontal association 
area. General principles of neivous action. Active organs as termini 
of all nervous impulses. Principle of facilitation. Principle of asso- 
ciation of centers of high tension. Diffusion as opposed to organiza- 
tion. Principle of progressive organization. 


Classification derived from study of nervous organs. Classification 
from observation superficial. Historical threefold classification. His- 
torical twofold classification. Classification according to nervous 
processes. Example of scientific analysis and classification. Relation 
of classification to introspection. Sensations. Reactions and atti- 
tudes. Fusion and perception. Memory. The process of ideation. 
Higher forms of action. Relation to historic classification. Practical 


Sensations not copies of external forces. Laws of sensation as one 
of the first problems in psychology. Relation of sensations to sen- 
sory nervous processes. Sensations as elements. Psycho-physics as 
a division of psychology. Meaning of term "quality. 1 ' Chromatic 
(or color) series and achromatic (or gray) series. Fundamental color 
names. The color spectrum and circle. Saturation, brightness, and 
mixtures. External light. Comparison of physical and mental series. 
Relation between the physical and the psychical facts dependent in 
part on the organs of sense. Evolution of organ of vision. Organ of 
sense as selective organ. The human eye Us muscles. The outer 
wall and the lens. Transparent media. Choroid coat. The retina. 
Rods and cones and their functions. Color blindness. Color-mixing. 
Pigment-mixing subject to physical law. After-images. Contrasts. 
Theories of color vision. Mrs. Franklin's genetic theory of processes 
in the retina. Physical sound. Pitch, or tonal quality. Intensity, or 
loudness. Complexity of a regular type the source of differences in 
timbre. Noise due to irregular vibrations. Evolution of the ear. The 
human ear, pinna, and meatus. The tympanic membrane. Air cham- 
ber on inner side of the tympanic membrane. Chain of ossicles. The 
inner car. The semicircular canals. The cochlea and sensory areas 


in the vestibule. Sensory cells in the cochlea. Contrast between 
auditory and visual processes. Meats, difference tones. Summation 
tones. Harmony not a matter of sensation. Absence of after-images 
in auditory sensations. Tone deafness. Taste and smell differenti- 
ations of a primitive chemical sense. Position of olfactory organ in 
the nasal cavity. Structure and function of the olfactory surface. 
Olfactory stimuli. Smell a rudimentary sense in man. Taste quali- 
ties and taste organs specialized. Organs of taste. Gustatory stimuli. 
Organs of touch. Differentiation of the tactual fibers; temperature 
spots. Pressure spots. Other "spots." Relativity of temperature 
sense; chemical and mechanical senses. Organs of touch at the 
periphery. Muscle sensations and organic sensations. Intensity a 
general characteristic. Weber's Law. General statement of the law. 
Mechanical explanation of Weber's Law. Other views regarding 
Weber's Law. 


All consciousness complex and selective. The selective character 
of conscious processes related to sensory impressions. Selective 
consciousness related to behavior. Common interests and their re- 
lation to behavior. Study of evolution of organs of action as impor- 
tant as study of senses. Evolution from gross muscles to highly 
differentiated muscles. Behavior dependent on nervous control. 
Coordination as necessary counterpart of differentiation. Individual 
development in behavior. Inherited coordinations or instincts. 
Glands as active organs. A constant tension of active organs 
as background of all behavior. Meaning of sensory impressions 
dependent upon inner conditions. Sensory processes and the 
equilibrium of action. Importance of sensations dependent on 
organization. Sensations unduly emphasized through introspection. 
Attitudes. Attitudes not related to sensations but to behavior. 
Relation of sensation to reaction. 

TUDES 146 

Reactions toward objects and reactions away from objects. Pleasure 
and displeasure. Cultivated feelings. Fear as a typical emotion. 
How to change the attitude of fear. Fear an emotion of complex 
beings. Fear and pathology. Parental love and altruism. Anger. 
Other emotions. Emotions as fundamental forms of experience. 
Higher forms of experience as related to behavior. Feelings of 
organic type. Flexor and extensor movements related to character- 
istic attitudes. Changes in circulatory movements as parallels of 
conscious changes. Disappointment as negative emotion. External 
attitudes. Attention as an attitude. Experiment to demonstrate 


tension. Various forms of attention. Sympathy with fellow beings. 
Sympathy involved in all recognition of objects. Illusion due to 
muscular tension. Such muscular tensions common to many experi- 
ences. All consciousness a form of sympathetic attention. Attitudes 
as related to higher processes of recognition. 


Sensory experience always complex. Sensation combinations or 
fusions. Space not a sensation, but a product of fusion. Tactual 
space as a simple example of fusion. Subjective and objective 
space. Perception and training. Development of spatial arrange- 
ments in the course of individual experience. Vision and move- 
ment as aids to touch. Tactual percepts of the blind. Wundt on the 
tactual perception of the blind. Lotzc's local signs. Inner tactual 
factors. Space not attached to any single sense. General conclu- 
sions regarding tactual space. Auditory recognition of location. 
Influence of movements in auditory experience of position. Quali- 
tative differences and localization. Distance of sounds recognized 
only indirectly. Unfamiliar sounds difficult to locate. Visual space 
and optical illusions. Effects of practice. Percepts always complex. 
Contrast. Common facts showing size to be a matter of relations. 
Physiological conditions of visual perception. Psychological state- 
ment. Photographic records of pcrcepted movements. Relation 
between size and distance. Definite optical relation between the 
distance and the size of an object and the size of the retinal image 
from this object. Berkeley's statement of the problem of visual 
depth perception. Experiments on binocular vision. Difference 
between the images in the two eyes. Stereoscopic figures and 
appearance of solidity. Retinal rivalry. Factors other than those 
contributed by the two eyes. Aerial perspective. Geometrical per- 
spective and familiarity. Shadows. Intervening objects. Depth a 
matter of complex perception. Relation to movements. General 
movements as conditions of fusion of retinal sensations. Space 
a system of relations developed through fusion. Movement and 
mechanical laws. Perception of individual objects. Mere coexist- 
ence of sensations no explanation of unity in the percepts of 
objects. Range of fusion determined by practical considerations. 
Changes in percepts through repetition. Parallel development of 
perception and habit. Time as a general form of experience. Ex- 
perimental determination of the scope of " the present." Scope of 
"the present" and its varying conditions. Time relations in verse 
and related systems of experience. Time arrangement as condi- 
tioned by the rhythmical changes in nervous processes. Perception 
more than the flux of sensations. Discussions of perception. 




Organic retentiveness. Remoter conditions of retention. Instincts. 
Protective instincts. Food-taking instinct. Instincts established 
through selection. Delayed instincts common. Impossibility of dis- 
tinguishing instincts from later-acquired forms of behavior. Habits 
from instincts and from independent conditions. Development of 
habit through conflict of instincts. Nervous development concerned 
in the selection of instincts. Habit as a modified instinct. Importance 
of heredity in explaining consciousness. Diffusion a mark of lack 
of organization. Development of habit from diffusion. Undeveloped 
movements. Diffusion analogous to all forms of overproduction. 
Conscious correlates of habit. Instinct, habit, and mental attitudes. 
Applications of the doctrine of attitudes to social science. 


Speech as a highly important special habit. Speech and ideas closely 
interrelated. Speculations regarding the nature and origin of speech. 
The special creation theory. The imitation theory. The interjection 
theory. Roots of language in natural emotional expressions and their 
imitation. Imitation. Other imitative communications of animals and 
man. Value of sounds as means of social communication. Limita- 
tion of forms of animal communication. The first stages of human 
articulation like animal cries. Articulations selected from the sum 
of possible activities. Evolution of ideas and speech. Gestures and 
broad scope of attention. Evolution of gestures in direction of sim- 
plification. Speech a highly specialized mode of behavior. Conse- 
quences of specialization. Speech an indirect form of behavior. 
Evolution of writing. Writing at first direct in form. Images 
reduced to lowest terms as powers of reader increase. Written 
symbols and their relation to sounds. The alphabet. Social motives 
essential to the development of language. Social system as source 
of the form of words. Social usage and the domination of individual 
thought. Social ideas dominate individual life. Experimental evi- 
dence of importance of words. Number terminology as a device 
for recording possessions. Symbols for groups of tallies. Parallel 
growth of number names and system of ideas. Development of 
arithmetic depends on an appropriate system of numerals. Social 
world unified through common forms of thought. Changes in words 
as indications of changes in individual thought and social relations. 
Illustration of change in w^rds. Words as instruments of thought 
beyond immediate experience. Images and verbal ideas. Mental 
attitudes as characteristic phases of verbal ideas. Other illustrations 
of thought relations. Concrete words. Examples of words arousing 
tendencies toward action. Abstract words. Contrast between con- 
crete images and abstract ideas. Particular images as obstructions to 
thought. Ideas or indirect forms of experience characteristic of man. 




The problem of describing ideas. Ideas not derived from present 
impressions. Ideas as revivals. Advantages of relative independ- 
ence of sensory impressions. Individual variations in imagery. The 
accidents of individual experience and mental imagery. Dependence 
on vividness and recency. The training of memory. Retention as 
distinguished from recall. Association by contiguity. Association 
by similarity. Association by contrast. New products evolved in 
ideation. Ideas not all images. Tendency to revert to imagery type. 
Advantages of indirect forms of experience. Animal behavior direct 
and perceptual, human behavior indirect and ideational. Influence 
of ideas on things. Tool-consciousness. Knowledge of nervous 
process limited. Consciousness as product of evolution. 


Adaptation through ideas. Early stages of barter. Barter perceptual. 
Standard values. Symbolic values. Evolution from perception to 
ideas. Higher controls of conduct. Ideational attitudes. Ideas as 
substitutes for impressions. Imagination as reorganization of ideas. 
Personifying imagination. Imaginations occasions of useless activi- 
ties. Critical tests of imaginations. Empirical test often, inapplica- 
ble. The test of internal agreement. The criterion of coherency a 
product of development. The demand for coherency as exhibited 
in constructive scientific ideas. Uncritical imaginations. Literary 
imagination and the canon of coherency. The uncritical forms of 
thought which preceded science. First sciences limited to facts 
remote from life. Scientific concepts. Validity of concepts. Abstrac- 
tion. Generalization. Judgments and reasoning. Logic. Primitive 
belief. Belief after hesitation. Belief a positive psychological fact. 
Spurious verbal belief. Habitual belief. Religious belief not in- 
stinctive. Sentiments not instinctive. Social life and the higher 
mental processes. Fields for the application of psychology of ideas. 


The idea of self sometimes regarded as matter of direct knowledge. 
Idea of self a concept. First stages of personal development not 
self-conscious. Gradual discrimination of self from things. Child's 
early notion of self largely objective. The idea of self as related to 
discrimination between the objective and subjective. The self dis- 
covered by contrast with not-self. Social consciousness and self- 
consciousness. The self at first not a scientific concept, but a 
practical concept. Cultivated self-consciousness. The religious 
motive for self-consciousness. Scientific idea of personality. The 
chief item in the concept of life the abstract idea of organization. 


Unity of self. The self as an efficient cause. Self as a valid scien- 
tific concept. Concept of unity. The self a concept. 


Disorganized personality in contrast with normal self. Illusions and 
hallucinations. Sleep, the influence of drugs, hypnosis, and insanity 
as forms of disorganization. The physiological conditions of sleep. 
The closing of avenues of stimulation in sleep. Various degrees of 
dissociation. Dissociation in the central processes. Dreams as dis- 
sociated groups of ideas. Dreams impressive only because they are 
uncriticized. Motor processes suspended by dissociations in sleep. 
Narcotic drugs dissociative in their effects. Effect of alcohol on 
the nervous system. Overexcitation is also dissociative. Toxic 
effects of certain diseases. These negative cases as evidences of the 
relation between normal consciousness and organization. Hypnosis 
a form of dissociation closely allied to sleep. Hypnosis as partial 
dissociation. Methods of inducing hypnosis. Hypnosis more readily 
induced after it has once been established in a subject. Various 
characteristics of the hypnotized subject. Ideas not subjected to 
criticism in hypnosis. Dual personalities in hypnosis. Dual per- 
sonalities in other than hypnotic conditions. Dual and multiple per- 
sonalities analogous to the various selves of normal life. Hypnosis 
a transient condition, insanity permanent. Movements sometimes 
normal in hypnosis, because the lower centers are not dissociated. 
The after-effects of hypnosis tend to become permanent. Insanity 
a permanent form of disorganization, introduced in many cases by 
dissociation and settling into an abnormal reorganization. Melan- 
cholia as a typical form of dissociation. Excessive excitation as a 
second typical case of insanity. Fundamental disturbances of in- 
stinctive and emotional life. Relation of psychiatry to psychology. 


Voluntary action a special form of behavior. Instinctive behavior 
different from voluntary action. Impulsive acts distinct from higher 
forms of voluntary action. Impulsive acts as phases of general mus- 
cular tension. Impulsive acts explicable through nervous organiza- 
tion. Impulse comparable to involuntary attention. Impulse and 
involuntary attention related to perception and habit. Simple case 
of choice. Behavior of the higher types dependent on ideas. Volun- 
tary action and its complex background as contrasted with lower 
forms of behavior. Decision a process of balancing ideas. Decision 
largely influenced by organization built out of past experiences. 
The meaning of prevision. The problem of the freedom of the will. 
Voluntary choice guided by purposes. Behavior of a higher type 



is related to education. Early scientific studies of behavior purely 
external. Purely external investigations not productive. Recent 
investigations and their stress on introspection and analysis of 
movement. Analysis of the form of movement. Concept of organ- 
ization as fundamental in all psychological studies. 


Hygiene a suggestive term for psychology. Relation of psycho- 
logical hygiene to physiological. Coordination of bodily activities. 
Control of excessive stimulations. Perceptual analysis. Perceptual 
synthesis. Dangers of specialization. Control of perceptual atti- 
tudes. Control of attitudes as a case of volition. Rules of whole- 
some ideation. Economy of mental effort. Preparation as aid to 
memory. Organization the key to all correct thought. The domi- 
nation of thought by some leading idea. Language of great im- 
portance in furnishing central ideas. The ineffectiveness of a 
detached verbal idea. Higher organization as a cure for verbalism. 
Self-directed organization as the goal of the higher mental life. 


Psychology a basis of scientific thinking about human conduct. 
Design in art as a psychological fact. Freedom in art. Architectural 
harmony analogous to musical rhythm and harmony. Literary art 
and psychological laws. Prose rhythms as related to the personal 
organization of writers. Verse another example of the same type. 
Literary content controlled by psychological laws. Feeling and 
intuition. Many of the social sciences predominantly objective in 
their methods. Introspective psychology and its limited support 
to social science. Interrelation of psychology and social science. 
Human evolution psychical. An hypothesis to explain the break be- 
tween man and the animals. Spencer's application of psychology to 
sociology. Relation of educational practices to scientific psychology. 
Psychology as a preparation for the intelligent diagnosis of particular 
situations which arise in educational practice. A curve illustrating 
the process of learning. Significance of a "plateau" in development. 
Other examples of the same type of development. Motor habits in- 
termittent. School training in its relation to the stage of develop- 
ment attained by the mind. Significance of scientific studies often 
indirect. Expression as an essential condition of mental life. Psy- 
chology historically a part of philosophy. Relation of psychology to 
philosophy closer than that of any of the special sciences. Psy- 
chology and logic. Psychology and aesthetics. Psychology and 
ethics. Psychology and metaphysics. 

INDEX 349 



1 . Diagram for use in demonstration of the blind spot .... 9 

2. Movements of a unicellular animal 1 6 

3. The hydra 18 

4. Much-enlarged section of a muscle cell and a sensory cell of a 

hydra, together with the connecting cells which lie between 
them 20 

5. Outline of a starfish, and nervous system of the same ... 24 

6. A stag beetle, showing the outline of the body and the dis- 

tribution of the nerve cells and fibers 25 

7. The nervous system of a frog as it would appear if the skin 

and muscles and protecting bone were removed .... 28 

8. Plate showing successive stages in the evolution of the verte- 

brate nervous system 31 

9. General form and position of central nervous organs ... 38 

10. Two nerve cells 39 

1 1 . A number of different types of connection between nerve fibers 

and cells 40 

1 2. The development in complexity of nerve cells in the course of 

animal evolution and in the course of the development of a 
single individual 41 

13. Transverse section across the spinal cord 42 

14. A diagram to illustrate the course of the sensory stimulation 

when it passes upward from the level of the spinal cord at 
which it is received 44 

15. A diagrammatic section through a part of one of the folds in 

the cerebellum 45 

1 6. The brain seen from below and cut open to show the paths of 

fibers from the cortex of the cerebrum to the lower organs 46 

1 7. Sketch showing some of the association fibers connecting vari- 

ous parts of the cortex of the cerebrum with one another 47 

1 8. A transverse section across the two hemispheres in a plane 

passing vertically through the cheek bones parallel to a 

line connecting the two ears 48 




19. Two sections representing portions of the cerebral cortex from 

two areas of the human brain 49 

20. A diagrammatic section showing the structure of the cortex 

of the cerebrum 50 

21. The outline of the lateral surface of the cerebrum with the 

typical convolutions, as given by Flechsig 52 

22. The median surface of the human cerebrum showing, as in 

Fig. 21, the various areas 53 

23. Color circle 76 

24. Wave forms 77 

25. A series of eyes which have reached various levels of 

development 82 

26. Diagrammatic section of the human eye 85 

27. A diagrammatic section of the retina 88 

28. Diagrammatic section showing the structure of the ear . . 104 

29. Diagrammatic section of the sensory cells in the vestibule . 108 

30. The structure in the cochlea as seen when a transverse sec- 

tion is made across the canal 109 

3 1 . Diagram to represent the f onhation of beats . . . . . . . 113 

32. The inner cavity of the nose 116 

33. Section showing the different cells which compose the mucous 

lining of the nose in the olfactory region 117 

34. Olfactory cells and supporting cells 1 1 8 

35. The depression between the sides of two papillae on the sur- 

face of the tongue 119 

36. A diagrammatic section of a single taste bulb showing the 

character of the different cells 1 20 

37. A diagrammatic sketch showing two neighboring taste bulbs 121 

38 A. Tactual end organs 1 24 

38 B. A Pacinian corpuscle 1 24 

38 C. A Missenian corpuscle 1 24 

39. Two Golgi-Mazzoni corpuscles of the type found by Ruffini 

in the cutaneous connective tissue of the tip of the 
human finger 125 

40. The complex distribution of a tactual nerve fiber in the 

immediate vicinity of a hair . 1 26 

41. Tooth of Gobinus showing distribution of nerve fiber through- 

out the canal of the tooth 127 



42. A highly developed muscle cell 134 

43. The contracted and relaxed state of a muscle 135 

44. Diagram showing relation of sensory impressions to reactions 143 

45. Involuntary hand movements made by the right and left hands 

of an observer who is thinking of a building situated in 

front of him 157 

46. Unaesthetical balance 158 

47. Miiller-Lyer illusion 172 

48. Illusion of contrast 1 74 

49. Zolmer illusion 1 76 

50. Poggendorff illusion 1 76 

5 1 . Figures showing the path followed by the eye of an observer 

in examining certain of the foregoing illusions . . . . 177 

52. Relation of retinal image to objects 179 

53. Binocular parallax 182 

54. An Ojibwa love letter 220 

55. Ancient and modern Chinese writing 221 

56. Derivation of the Roman letter M from the ancient Egyptian 

hieroglyphic owl 222 

57. Association by similarity 245 

58. Fatigued cells 280 

59. Curve showing the intensity of sound necessary to awaken a 

sleeper at different periods of sleep 282 

60. Curves for sending and receiving telegraphic messages . . 338 

6 1. Analysis of the receiving curve 340 




Psychology a study of conscious processes. "The under- 
standing, like the eye, whilst it makes us see and perceive 
all other things, takes no notice of itself; and it requires 
art and pains to set it at a distance, and make it its own 
object." 1 Thus did one of the earliest English psychologists 
point out the distinction between ordinary experience and 
the scientific study of mental processes. A man may be 
afraid, or enthusiastic, or lost in reverie ; in each case his 
mind will be full of emotions and ideas, but he will not be 
led by the intensity of his experiences to make them sub- 
jects of analysis and explanation. Indeed, the more he is 
absorbed in the experience itself, the less likely he is to 
psychologize about himself. We all have the raw materials 
for a science of mental processes within us, but we require 
special motives to lead us to that careful study of these 
processes which gives rise to the science of psychology. 

The motive of wonder. The motives which have led men 
to make a scientific study of their conscious processes are 
numerous and varied in .character. Perhaps the most com- 
mon of these motives is to be found in the exceptional and 
baffling experiences through which one passes from time to 
time. I think I hear a voice, but find on examination that 
no one spoke. I try to grasp an object, but find that for 

1 John Locke, Essay concerning Human Understanding, Bk. I, chap, i, 
sect. i. 


my sense of touch the thing is not what it seems to be for 
my sense of vision. Such experiences as these require some 
explanation, and even the most superficial observer is likely 
to become interested, at least for the moment, in their inter- 
pretation. Popular psychology seldom gets beyond this ex- 
amination of striking and unique experiences ; consequently 
the notion has gained wide currency that psychology is 
devoted entirely to the investigation of occult phenomena. 

Discovery of individual differences as motive. Interest in 
exceptional experiences is hardly a sufficient motive, how- 
ever, to lead to long-continued systematic study. It is to be 
doubted whether psychology would ever have developed into 
a serious science unless other more fundamental motives 
had arisen to turn the attention of men to the examination 
and explanation of their conscious processes. The more 
fundamental motives began to appear as far back as the time 
of the Greeks. These early thinkers found themselves in 
bitter intellectual controversies. Given the same facts and 
the same earnest effort to use these facts in the establish- 
ment of truth, the Greeks found that two individuals often 
arrive at opposite conclusions. This made it clear that like 
facts may lead in two different minds to entirely different 
processes of thought. So striking were the individual dif- 
ferences that early thinkers despaired of finding any general 
laws. Gradually, however, as the way in which men remem- 
ber and the way in which men relate their ideas were studied, 
it became apparent that back of the seeming variety there 
are certain common forms of consciousness, certain funda- 
mental laws of mental activity which can be discovered and 
systematically arranged into a science of mental life. To this 
task the Greek philosophers set themselves with enthusiasm, 
though with inadequate methods, and out of their efforts arose 
the earliest schools of serious psychological investigation. 

Differences between experience and physical facts. An- 
other fundamental motive appeared early in the modern 


period as a direct outgrowth of the discovery that there is 
a disparity between the facts discovered by physical science 
and the. direct testimony of consciousness. Thus Sir Isaac 
Newton discovered that he could break up white light into 
all the colors of the rainbow. Conscious experience of 
white light is, on the contrary, absolutely simple and unana- 
lyzable. Even among the students of physical science there 
had never been any hesitation up to the time of Newton 
in assuming that external white light is just as simple as 
human , consciousness of whiteness. The ancients had a 
definite explanation of vision which shows that they explic- 
itly believed in the simplicity of external white light.- Light 
was for them a series of particles emanating from the object 
and entering the eye. When they saw white, they believed 
that the experience was due to white particles in the eye, 
and that these white particles came from a white body. All 
was uninterrupted likeness from the physical object to con- 
sciousness. Such an explanation of white light as that 
offered by the ancients was rendered utterly untenable by 
Newton's discovery. When further investigations led physi- 
cists to define light and other forms of physical energy 
as modes of vibration, the breach between conscious experi- 
ence and external reality became so wide that men felt com- 
pelled to study conscious experience as well as physical facts. 
It is noteworthy that the period during which Newton and 
his successors were making their discoveries in physics was 
a period of the profoundest interest in psychological problems. 
Place of consciousness in evolution. As reinforcements 
to the impetus given to psychological study by discoveries 
in physics, new motives for such study arose with the 
development of physiology, and especially with the estab- 
lishment of the biological doctrine of evolution. Every 
highly developed function of an animal is recognized in 
biology as having its relation to the struggle for existence. 
If an animal can run well, we find this ability serviceable 


in saving the animal from enemies, or in helping it to 
procure food. If an animal has keen vision, we find that 
the animal depends on this sense in the essential activities 
of life. With such facts clearly before us, we cannot escape 
the question, What part does consciousness play in the 
economy of life ? From the lower forms of animal life up 
to the highest, we find a steady increase in the scope of 
intelligence. In the highest animals we find mental evolu- 
tion carried so far that intelligence is very often of more 
significance than any other single function or even group 
of functions. Certainly this is true of man. The digestive 
functions of a man differ very little from those of the 
higher animals ; the muscles and bones and organs of cir- 
culation in man are very much like those of his near rela- 
tives in the animal kingdom. In matters of intelligence, on 
the other hand, man has never been in any doubt as to the 
wide difference between himself and even the highest of 
the animals. Man lives in a world of ideas from which 
animals are excluded by their lack of intelligence and by 
their lack of that means of social intercourse which is the 
possession of man alone, namely, language. Furthermore, 
in his dealings with the physical world man discovered the 
use of tools through which he has been able to reshape his 
environment. Man has, in short, through his conscious 
activities, attained to a mode of struggle for existence which 
is unique. We cannot understand and explain human life 
and human institutions without studying the facts and laws 
of consciousness, without raising the question of the relation 
of consciousness to all of man's other attributes. 

The first method of psychology. The methods of psy- 
chological investigation have progressed with the rise of 
each new motive for the study of conscious life. At first, 
the method was one of direct self-observation. This method 
is known as introspection. When one has an emotion, others 
may see its external expressions, but only the man himself 


can observe the conscious state which constitutes the emo- 
tion. In looking inward and observing this conscious state, 
one is said to introspect. 

The early psychologists were so impressed with the 
importance of introspection that they regarded it as the 
sole method of collecting facts for their science. They thus 
seriously limited the scope of their studies. Mental proc- 
esses are fully understood only when the relations of these 
inner events to the outer world are taken into account. 
When a man meets his friend and greets him, the psychol- 
ogist is interested not only in the inner fact of conscious 
recognition but also in the impression made on the eye, for 
it is in this impression that recognition originates ; further- 
more, the psychologist must study the bodily activities of 
greeting which follow recognition. Indeed, the most pro- 
ductive discoveries of modern psychology have come from 
a study of the setting in which conscious processes belong. 

Nervous processes as conditions of consciousness. Thus 
we see that among the facts which are not open to intro- 
spection but are of importance in explaining consciousness 
are the processes which go on in the organs of sense and 
in other parts of the nervous system. One cannot introspect 
brain processes, but much light has been thrown on the way 
in which men think by a study of both the structure and 
action of the brain. 

Studies of behavior. Another type of indirect or non- 
introspective investigation which has of late been culti- 
vated with very great advantage to psychology deals with 
the facts of human and animal behavior. Here, as in the 
examination of the nervous activities, it is possible to dis- 
cover certain stages of development and to relate these to 
the well-recognized general fact that there are progressive 
stages of intelligence in the animal kingdom. 

If these and other modes of indirect study of mental life 
are judiciously added to introspective observations of one's 


own conscious processes, psychology loses nothing of its 
directness, and it gains much in breadth. 

Overemphasis of slower forms of mental activity through 
introspection. A further advantage which is secured by rec- 
ognizing that introspection is not the only possible method 
of collecting psychological facts is that the experiences most 
directly open to introspection are thrown into a truer per- 
spective by the combination of indirect and direct examina- 
tion. The student who depends solely on introspection will 
give the largest share of his attention to that which is in the 
foreground of consciousness, usually to some complex mental 
process which passes slowly across the stage ^of conscious- 
ness. He will often give undue weight to some single 
experience because it is so clear, adopting this clear experi- 
ence as typical, and depending *upon it for the explanation 
of many of the less obvious facts of mental life. For exam- 
ple, when one hears a word and stops to consider deliber- 
ately the conscious process by which he interprets the word, 
he is very likely to experience a series of memory images 
which follow upon the word and give it meaning. Thus, let 
the reader ask himself what he thinks of when he sees the 
word " house." The more carefully he searches in his con- 
sciousness, the more he becomes aware of trains of memory 
images. Many psychologists having made this introspective 
observation set it down as a general fact of all mental life 
that the process of recognition always consists in the revival 
of trains of memory images. If the skeptical observer ven- 
tures to say that he does not find in his ordinary recognition 
of words such attendant trains of memory images, he is 
reproved for incomplete introspection. When we come to 
the problem of recognition of words in our later discussions, 
this question will be taken up in detail, and it will be shown 
that what is needed is not a formula borrowed from the 
more elaborate, easily introspected case, in which recogni- 
tion is slow and long drawn out. What is needed is a 


formula derived from a study of habit. When we become 
very familiar with an object we are less and less likely to 
attach to it trains of images ; we respond to it promptly and 
skillfully without waiting for a full picture to be developed 
in the mind. So it is also with words. The more familiar 
the word, the less the mind delays and pictures its mean- 
ings. This example shows that psychology must not adopt 
as its chief bases for explanation the long-drawn-out mental 
processes which furnish the most content for introspection. 

Experiment in psychology. When psychology is recog- 
nized as a broad science, dealing with many facts related 
to consciousness as well as with consciousness itself, it will 
be understood why recent studies in this field have made 
liberal use of experimental methods. Experiment became 
a conspicuous method in psychology about fifty years ago. 
Prior to that time the observations of psychologists were 
limited by the opportunities of personal experience. 

Let us see the advantages of deliberate experimentation 
by canvassing an example. A psychologist is studying 
memory. He notes, when he tries to recall objects which 
he has observed, that there is a certain incompleteness in 
his mental reproduction and that this incompleteness be- 
comes increasingly impressive with the passage of time. He 
will hardly fail to find out by this sort of self-observation 
much that will help him in describing his processes of 
memory. Suppose, however, that he wishes to find out 
with definiteness the law which memory exhibits in its 
decay, or suppose that he wishes some final decision as to 
the best way of examining groups of objects in order that 
he may carry away a complete and permanent memory of 
them. He will find it advantageous for this more complete 
study to arrange the objects with a view to the questions 
which he wishes to answer. He will observe the objects 
during a fixed period, and after a known interval will 
submit his memory to a definite test. This illustration is 


sufficient to show that there are advantages in the precise 
control of the conditions of observations, which is the first 
step in experimentation. If, now, the psychologist adds 
certain aids in the way of apparatus which will make it 
easy to record the time intervals and to present the matter 
to be memorized in absolutely uniform fashion, it will be 
recognized at once that the more fully developed and pre- 
cise method of investigation leads to a degree of accuracy 
in ascertaining the facts which is otherwise quite impos- 
sible. The experimental method also makes it possible for 
observers remote from one another to collect their observa- 
tions under the same conditions, so that they can compare 
their results and generalize the information which they have 

There has been much discussion as to the exact place of 
experiment in psychology, some holding that it is the only 
true scientific method, others holding that it is very limited 
in its application. Those who are most devoted to experi- 
mental methods have sometimes gone so far as to assert 
that experimental psychology is a separate discipline. Those 
who criticize the method point out that the profounder 
emotions, such as intense sorrow, and the higher forms of 
abstract thought, such as are involved in a scientific dis- 
covery, cannot be produced and modified at will. Both 
extreme positions are to be avoided. Carefully prearranged 
observation under controlled conditions, wherever this is 
possible, is the true ideal of scientific psychology. Where 
experiment is not possible, other forms of observation must 
and should be employed. 

Explanation at variance with mere observation. It may 
be well, both for the sake of defining the scope of psychol- 
ogy and for the purpose of illustrating its methods, to call 
attention to the fact that this science, like other sciences, 
frequently brings out in its explanations facts which seem 
to run counter to direct observation. Thus, before we study 


any of the physical sciences, we observe that the surface of 
the earth about us is apparently flat. As we progress in 
science we come on facts which are incompatible with the 
notion that the earth is flat. We note all these observations 
and compare them, and finally accept as our general scien- 
tific conclusion the statement that the earth is spherical and 
not flat, as it seems to ordinary observation. Again, we do 
not hesitate to accept the dictum of science that the earth is 
moving at a tremendous rate, although we do not observe 
the movbmcnt directly. These illustrations go to show 
that scientific conclusions are broader in scope than single 
observations, and frequently so different from the single 
observations as to constitute essentially new facts. 

FIG. i. Diagram for use in demonstration of the blind spot (see page 10) 

When we leave physical science where we have learned 
easily to accept the results of inference, and turn to psy- 
chology, we do well to remember that earlier generations 
less trained in the methods of science found it difficult, 
indeed quite impossible, to substitute inferences about the 
shape and motion of the earth for the facts of sense ex- 
perience. We should therefore be prepared by the con- 
sideration of these analogies to recognize the necessity of 
comparison and interpretation in our psychology and to 
overcome our own hesitation in accepting psychological 
inferences as substitutes for introspective observations. 

A simple mental experience which offers an excellent 
opportunity for the application of the principle of inference 
is as follows : Let an observer close one eye and look with 
the open eye at the printed page before him. He will 
undoubtedly observe what seems to be an uninterrupted 


series of impressions coming to him from all parts of the 
page. This is, however, quite as incomplete a description 
of the facts as is the description of the earth's surface 
based upon direct observation. To demonstrate this, let 
the observer close or cover the left eye and look steadily 
with the right eye at the small cross in Fig. I. Now let 
him move the book backward and forward from seven to 
eight inches in front of his face until the black circle dis- 
appears. He will thus discover that a certain part of the 
page is not yielding an uninterrupted series of impressions. 
The explanation of the facts here involved cannot be ob- 
tained through introspective observation, for it depends on 
the structure of the eye, there being in the sensory surface 
of the eye an area that cannot receive impressions. This 
is the area where the optic nerve leaves the eye. This illus- 
tration should prepare the student to find in the science of 
psychology many statements about the nature of his conscious 
processes which he cannot expect to verify by a simple proc- 
ess of observation. Observation is indispensable, but the sci- 
entific understanding of consciousness requires an elaborate 
interpretation of all the facts which can be obtained. 

Subdivisions of psychology. Psychology as a science 
dealing in a broad way with conscious processes and with 
the conditions and results of these processes has proved 
to be most fruitful in its applications. Wherever human 
nature is to be influenced, whether it be in the writing of 
an advertisement or in convincing a jury, the psychology of 
the process is worth understanding. If the study of the 
process can be made exact through experimentation and 
comparison, applications will be the safer and more effec- 
tive. There has been in recent years a vigorous cultivation 
of psychology in all its possible forms and in all its possible 
applications. Thus, there is a psychology of animal con- 
sciousness. There is a psychology of the child's conscious- 
ness, especially cultivated by those who wish to ascertain 


the laws of mental development which underlie education. 
There is a psychology of abnormal human minds known by 
the special name of psychiatry. There is a psychology of the 
products of human minds when they act in social groups, 
as in the development of language, customs, and institutions. 
This is called social psychology or folk psychology. Certain 
other lines of subdivision are sometimes drawn. Thus, 
experimental psychology has sometimes been marked off 
from other forms of investigation. Physiological psychology 
has also been treated as a separate science. Finally, it is 
not uncommon to meet such titles as the psychology of art, 
or of literature ; the psychology of religion, of the crowd ; 
and so on through a long list of highly differentiated 

Some confusion has resulted because of the tendency 
of psychology to break up into so many minor disciplines. 
The confusion disappears, however, as soon as one recog- 
nizes that in methods and subject matter all the special 
psychologies are merely parts of the general science. The 
explanation of the subdivisions is partly historical. As new 
interests or new methods have asserted themselves, the 
traditions of the earlier stage of psychology have often 
resisted the innovation to such a degree that a new disci- 
pline was for a time necessary to accomplish the develop- 
ment of the science. In addition to these historical reasons, 
the breadth of human interests in the study of experience 
is so great that the mastery of any single phase of mental 
life involves a concentration somewhat more pronounced 
than that which is required in many sections of the physical 

Summary and definition of psychology. The special de- 
partments of psychology cannot all be fully treated in a 
general course, such as that which is to be given in the 
following chapters. Much can be touched upon only by way 
of illustration. The general treatment must confine itself to 


the establishment of broad principles applicable in greater 
or less degree to all of the special fields. With this neces- 
sity of general exposition in mind, the statement with which 
this introductory chapter began may be amplified as follows : 
The legitimate function of a course in general psychology 
is to consider the typical processes of mental life with refer- 
ence to their internal constitution and also with reference to 
their external conditions ; to examine these processes with 
the aid of experiments and observations from both the intro- 
spective and impersonal points of view ; and, finally, to relate 
consciousness to the other phases of life, especially to human 
and animal behavior, and also to external reality in such a 
way as to furnish the basis for an adequate understanding 
not only of individual consciousness but also of the experi- 
ence of all conscious beings. 

Definitions of certain general psychological terms. In this 
statement and throughout the chapter the terms "conscious- 
ness," "mental life," and "experience" have been used with- 
out any effort to define them. Complete critical definitions 
of these terms presuppose a knowledge of the results of 
psychological study, for it is the function of psychology to 
ascertain the characteristics of consciousness. In the mean- 
time there is no danger of confusion in the preliminary use 
of the terms. Consciousness is what each one of us has 
when he sees and hears, when he feels pleasure or sorrow, 
when he imagines or reasons, or decides to pursue a line of 
action. Experience is a general word which may conven- 
iently be used to cover the same group of facts. Stones do 
not experience impressions or emotions. Man, on the other 
hand, lives in a world of experiences. His inner life is not 
made up of objects, but of experiences of objects. When- 
ever we think, or remember, or try to understand an object 
presented to the senses, we have an experience. As pointed 
out in the discussion of introspection, conscious processes 
may be distinguished from other facts by the possibility of 


self-observation or introspection, by which method alone 
these conscious facts can be directly observed. Facts of 
external reality are open to general observation by many 
different individuals ; conscious experiences are purely per- 
sonal, open to introspective observation only. We sometimes 
express the contrast between the facts of conscious experi- 
ence and the facts of external reality by the use of the terms 
"subjective" and "objective." Whatever belongs exclusively 
to the world of experience is called subjective. Thus, ideas 
and feelings are subjective. The facts with which physics 
and chemistry deal are not exclusively subjective ; they have 
objective, external characteristics. Indeed, physics and chem- 
istry are interested in facts only in so far as they are objec- 
tive. For these natural sciences the subjective ideas of the 
individual physicist or chemist are merely the means to an 
end, which end is the intelligent comprehension of the ob- 
jective world. The same antithesis which is expressed by 
the terms " subjective " and " objective " is expressed by the 
terms "psychical facts" and "physical facts." The former 
are the directly known conscious processes; the latter are 
the facts of the external world as known through the senses 
and as studied in the objective sciences. These remarks c|n 
the various terms which are used in defining the sphere of 
psychology serve to indicate, in a sufficiently unambiguous 
way, the direction in which our studies must turn. 



The introspective approach. There are two lines of pro- 
cedure which may be adopted in the study of mental proc- 
esses. On the one hand, we can begin with the description 
of some personal experience and from this central fact move 
outward until we arrive at a full explanation of all the causes 
and conditions of this experience. Thus, when I try to re- 
member the name of a person whom I met some time ago, 
I find that I can recall the vague general fact that it was 
a short name, beginning with the letter " E," but it requires 
time and effort to fill in the rest. The questions which im- 
mediately arise are such as these : Where is the storehouse 
in which these memories were locked up ? Why did one 
part of the name drop away and another part persist ? What 
kind of effort is necessary to bring out the missing part? 
Evidently it will be necessary, before these questions can 
be answered, to go outside of immediate consciousness. 

Indirect method of approach to psychological facts. The 
second line of procedure is the reverse of that just de- 
scribed. We can approach personal experience from without, 
reviewing briefly the conditions which make such experi- 
ence possible and gradually coming to the particular facts 
which at this moment fill the observer's mind. This mode 
of taking up the study has the disadvantage of leaving 
the student with the impression that psychology is very 
remote from his inner experiences. On the other hand, it 
has the advantage of supplying him from the first with a 



body of facts which he is not able to contribute out of his 
direct observation of himself. Some patience will be required 
in coming thus indirectly to the study of mental processes, 
and the student will need to keep in thought, with very little 
aid from the text, the goal toward which the preliminary 
study is leading. 

The indirect method is the one with which we shall be- 
gin. We shall take up, first, the facts of animal behavior 
and nervous organization and shall thus lay the foundations 
for an explanation of the facts of personal experience. Later 
we shall review the facts of consciousness itself in the light 
of this preliminary indirect study. 

Characteristics of unicellular animals. Our method car- 
ries us back to the most primitive forms of animal life. 
Here we find minute microscopic beings whose whole body 
consists of a single cell. This cell is made up of a mass 
of living tissue known as protoplasm. Such a unicellular 
animal is capable of moving about by contracting its tissue ; 
it is capable of reproducing itself by cell division ; it is capa- 
ble of digesting food and throwing out waste matter ; and, 
finally, it is irritable when acted upon by external forces. 
When the student examines life reduced to the low terms 
which are exhibited in a unicellular animal, he realizes 
more fully than he is likely to realize when examining 
higher forms how thoroughly interdependent are all the 
phases of an animal's life. Consider how impossible life 
would be without the new supply of energy which comes 
through digestion ; how limited in scope life would be with- 
out movement to bring the animal to new sources ef food 
and carry it out of danger, or without cell division to in- 
crease the number of members in the species ; and how 
utterly out of contact with the rest of the world the indi- 
vidual would be without irritability. The fact that all these 
functions appear in the simplest unicellular forms shows 
how fundamental they are. 



Simplest types of behavior. The only facts on which we 
can base a judgment with regard to the inner processes in 
such an animal are the facts of behavior. These appear to 
be very simple. The animal has three forms of movement. 
It swims forward and takes in food. If it encounters a 
stimulus which is unfavorable, such as heat or acid, it darts 
backward and swings around in a direction which takes its 
mouth opening away from the stimulus. Fig. 2 shows a 

series of movements as exe- 
cuted by such an animal. The 
figure represents one end of 
a microscope slide which is 
heated at the upper edge. 
A unicellular organism, Oxyt- 
richa, in the position I is 
reached by the heat coming 
from the upper part of the 
slide. The animal reacts by 
turning to the right (position 
2). This intensifies the exci- 
tation caused by the heat, and 
the animal backs to position 3. 
It then turns (position 4) and 
swims forward (position 5), 
again encountering the heat. 
It then darts back (position 6), turns (position 7), and swims 
forward until it comes against the w^ll of the trough (posi- 
tion 8). It then reacts as before, by backing (positions 8-9), 
and turning to the right (positions 9-10). This type of 
reaction continues as long as its movements carry it either 
against the wall or into the heated region. When it finally 
gets away, as it must in time if it continues its reactions, 
it swims forward, taking food as it did before disturbed. 
Thus we see that there are in the lowest animals very limited 
possibilities of behavior. 

FIG. 2. Movements of a unicellular 
animal. (After Jennings) 


Consciousness no more complex than behavior. This 
meager repertoire of behavior betokens a relatively undif- 
ferentiated inner life. Yet even this animal is influenced 
by the impressions made upon it by the outer world. We 
may think of the heat as setting up a commotion among 
the molecules which make up the body, and this inner 
commotion results in a recoil. We distinguish between the 
irritability of the animal and its power of movement, but in 
reality these two functions are one. The animal recoils 
because it is internally aroused by the heat. Once the 
extraordinary condition is removed, the animal begins to 
exhibit its more peaceful form of behavior, namely, that 
of swimming forward, this evidently being the natural ex- 
pression of its calmer inner condition. 

It is hardly possible for us to imagine, in terms of our 
own consciousness, what must be the inner experience of 
such an animal, if, indeed, we have any right to think of 
it as having experience. Certainly a unicellular animal can 
have discriminations only of the grossest sort. When all is 
well and the animal is swimming forward and taking food, 
the inner state must be one of well-being. When the shock 
of a strong stimulus comes, there must be a kind of vague 
inner excitement. The two inner states probably differ just 
in the degree in which the forms of behavior differ. 

Behavior more limited than sensitivity. If we study such 
animals with respect to irritability, we find that they respond 
to various forms of external energy. Thus, if light falls on 
the water, some species will collect in the darkness, others 
in the light, in such numbers as to indicate clearly, in either 
case that they are affected by the light. Again, pressure 
due to contact with external objects, as shown above, and 
also vibrations of the water are effective in producing more 
or less intense movements. Acids or other strange chemical 
substances in the water will produce reactions similar to 
those called out by heat. In all these cases the animal 



exhibits only a few fixed forms of reaction. Our inference 
is that the inner processes aroused by all the different 
forms of energy are alike. The further inference is that the 
animal discriminates between that which calls for forward 

movement and that which calls for 
withdrawal, but is not able to make 
any finer discriminations. 

The study of unicellular organ- 
isms leaves us, then, with four 
important general facts on which 
to base our study. Irritability is 
a fundamental function of even 
the lowest forms of protoplasm ; 
it is at first very little differenti- 
ated ; it is the function which 
guides the animal in its responses 
to its environment ; and, finally, 
the description of behavior is a 
very direct means of arriving at 
an understanding of the inner 
processes of irritability. 

Specialization of cell structures 
and functions in higher animals. 
Turning now from the unicellular 
animal to a form somewhat higher 
in the scale, we find that structur- 
ally the more highly developed 
animals are characterized by the 
fact that their bodies, instead of 
consisting of a single cell, consist of an aggregation of cells ; 
this we express by the statement that they are multicellular or- 
ganisms. Fig. 3 represents a section of a simple multicellular 
animal which lives in fresh water and is known as a hydra. 
The animal is sack-shaped, with a mouth opening and ten- 
tacles at its upper end. The figure shows the walls of the 

FIG. 3. The hydra 

The figure shows a section through 
the body and exhibits the two cellu- 
lar layers with a neutral layer 
between. The general body cavity 
G is lined by cells which are 
devoted entirely to the special 
function of digestion (the mouth 
opening is at M). A*, R, ^?, K 
are the reproduction cells. The 
outer wall of the body is made 
up of muscle cells and specialized 
sensitive cells. T, T, T are the 
tentacles. (Adapted from Haller) 


sack-shaped body much magnified. The inner lining of this 
wall is made up of a layer of cells which are specialized to per- 
form the function of digestion. The outer wall is specialized 
in certain of its cells for the reception and transmission of 
stimulations, and in other cells for the performance of move- 
ments. The processes of reproduction are provided for at 
special points in the body wall as indicated at R, R, R, R 9 
in Fig. 3. Between the inner and outer layers there is an 
intermediate layer of tissue, in which cells sometimes appear 
from one of the primary layers. The intermediate layer is not 
sufficiently developed to constitute a separate series of organs. 
The multiplication of cells and specialization of functions 
here exhibited have advantages familiar to anyone who has 
observed the analogous fact of division of labor in social 
organizations. The cells of the body which are set apart for 
special purposes do not lose the general characteristics which 
belong to all living protoplasmic cells. For example, all the 
cells of the body absorb the necessary nutrition to support 
their individual lives, but the cells outside of the digestive 
layer do not take their nutrition from the external world; 
they derive it from the digestive cells which alone perform 
the special function of digesting foreign particles. So also 
with the function of irritability. This is not lost by the 
specialized contractile cells and digestive cells ; it is merely 
reduced in these cells to a very low point and is very highly 
developed in the specialized sensitive or irritable cells, so 
that the movement cells or muscle cells and all other parts 
of the body come ultimately to receive their impressions 
from the outer world, not directly, but through the neural 
or sensory cells. The neural cells or nerve cells are special- 
ized cells which take over the function of irritability. They 
are placed in the outer body wall, where they are in the 
most favorable position to be acted upon by external forces 
or stimuli, as forms of energy which affect the nervous sys- 
tem are technically called. They develop a more complex 



chemical structure than the other cells of the body, so that 
they are more easily set in action by external forces. They 
are, accordingly, highly important, but by no means inde- 
pendent factors in the organic economy. They are developed, 
not for some remote and separate life of mere irritability or 
sensitivity, but as essential parts of the developing organism, 
acting as paths through which external forces enter the body 
and cause inner states which will adapt the animal in its activ- 
ities to the world in which it lives. 
Even in the simple organism 
under consideration, the process 
of specialization has advanced so 
far that there begin to appear 
various classes of neural or irri- 
table cells, each serving a special 
function. Certain of these cells 
serve the direct function of receiv- 
ing impressions from the outer 
world, and are known as sensory 
cells, while others serve the func- 
tion of transmitting the impulse to 
the muscle cells. Fig. 4 shows a 
much-enlarged section of the outer 
body wall of a hydra. M is a mus- 
cle cell, heavy and elongated to 
make more effective the contractile 
function. 5 is a sensory cell which receives impressions. 
C, C, C y Care intermediate transmitting cells, and F, together 
with the other fibers shown, carry the impression through C 
from 5 to M. 

Specialized nervous processes. The process which goes 
on in the neural cells may be described as follows : Some 
form of external energy acts upon the cells. The external 
energy, as noted above, is called a stimulus. This sets up 
a chemical process in the cell which is known as a process 

FIG. 4. Much-enlarged section 
of a muscle cell and a sensory 
cell of a hydra, together with 
the connecting cells which lie 
between them 

M, muscle cell; S, sensory cell; 
C, intermediate cells ; F y fiber 
connecting the sensory cells with 
the central cells. (Adapted from 


of excitation or a stimulation. The process of excitation 
liberates energy which was stored up in the cell. This 
liberated energy is transmitted to other cells in the body, 
either to the secondary transmitting neural cells, C t C, or to 
the active contractile cells such as M. This current of 
nervous energy has been compared to an electric current. 
It is, however, much slower than an electric current, its rate 
of transmission being in the higher animals about one 
hundred meters per second or less. We do not know its 
exact character, but probably it is more like the succession 
of combustions which takes place along the line of a fuse 
of gunpowder. Our ignorance of the exact nature of the 
nervous current need not delay the discussion, however, for 
we shall find that the importance of nervous currents 
for our further study depends upon their paths of trans- 
mission rather than on their chemical nature. The path of 
transmission will be determined primarily by the direction 
and connections of the fibers which unite the cell in which 
a given excitation originated with other parts of the body ; 
secondarily, the path of transmission will depend on the 
fatigued or unfatigued condition of the cells and on the 
other currents of energy which are flowing through the system 
at the same time. All these complex possibilities may be 
summed up in the statement that in its transmission through 
the neural organs every nervous excitation is directed and 
is combined with other impulses, and is ultimately determined 
in its effects by its path of transmission to the muscles or 
glands and by its relation to other impulses. Furthermore, 
as soon as it is recognized that nervous impulses consist in 
currents of energy which have been liberated by the stimulus, 
it will be recognized that every nervous current must pro- 
duce some effect before it is dissipated ; for a current of 
energy must do some work it cannot disappear. The 
effects produced by nervous impulses are of two kinds. 
First, the energy may be absorbed in the course of its 


transmission, in which case it will produce changes in the 
condition of the nervous tissue, thus contributing to the 
modification of the structure of that tissue. Second, it may 
be carried to the natural outlet of all nervous excitations, 
namely, the active organs of the body, where it will produce 
some form of behavior. If it contributes to changes in 
structure, these changes in structure will ultimately influ- 
ence new incoming impulses which are on the way to the 
active organs. We may therefore say that, directly or in- 
directly, all incoming nervous impulses are transmitted to 
the active organs of the body after being more or less 
completely redirected or partially used to produce structural 
changes in the nervous organs. 

Nervous processes of three distinct types. The range of 
nervous processes possible in the simple structures of a 
hydra is extremely limited ; for this very reason the funda- 
mental characteristics of nervous processes are all the more 
apparent. We can distinguish clearly the first step which 
is the reception of the external stimulus. This first step 
is commonly described as a sensory nervous process. The 
cell on which the stimulus acts is a receiving cell. The in- 
termediate cells placed between the receiving cell and the 
muscle are called transmitting cells or central cells. The 
fibers passing from the central cells to the muscle or gland 
are motor fibers. It will be seen that the sensory, central, 
and motor processes cannot be sharply distinguished from 
each other; they are all phases of a single continuous 
process, the end of which is always some active process in 
the muscles ; but for purposes of scientific explanation it is 
necessary to distinguish them as three distinct types. 

Behavior varied and much more complex. If we contrast 
the hydra with the unicellular organism studied in earlier para- 
graphs, we are at once impressed by the fact that the hydra 
has a greater variety of forms of behavior. To be sure, all 
these forms of behavior belong under two fundamental types, 


namely, that of moving forward to capture food and that of 
withdrawing from danger. But each of these fundamental 
forms of action has been developed so that it is more 
elaborate and varied than it was in the unicellular animal. 
Thus the tentacles move in such a way as to sweep food 
into the mouth, and they contract in the presence of 
unfavorable stimuli, even when the body as a whole is not 
in full action. The body moves sideways, now in one 
direction, now in another. In short, the more complex 
animal is characterized by an increasing variety of action. 

Not only so, but an action often consists of a series of 
related movements, making a complex chain of acts, all 
directed toward a single end. The body, for example, 
comes in contact with a piece of food. The animal swings 
around, the tentacles seize the particle, sweep it into the 
mouth, and the inner digestive canal closes in on it and 
begins its ingestion. Such a chain of cooperating acts 
shows that a high level of evolution of behavior has been 
reached where single elements of behavior are united into 
complex coordinations. 

From this point on we shall dwell chiefly on the structural 
growth of the nervous system, but the statements made 
regarding the behavior of hydra should be thought of as 
repeated and even as amplified to correspond to each 
progressive complication of nervous structures. 

Progressive evolution in both structure and behavior. 
When we turn from the hydra to the higher forms of life, 
we find that the multiplication and specialization of cells go 
on to the highest degree, producing in the animals at the 
upper end of the scale a variety of forms of sensitivity and 
of behavior which culminate in such capacities as those 
exhibited in man. 

Centralized nervous system. We must confine our survey 
to a few of the major facts in this process of evolution. As 
we ascend the scale, there is a grouping of the central cells 


into complex organs and, second, a differentiation of the 
receptive or sensory cells resulting in the production of 
special organs for the reception of a great variety of stimuli 
such as light, sound, tastes, odors, and other forms of 
energy. These two types of development may advantageously 
be considered in succession. For the remainder of this 
chapter, the differentiation of the sense organs will be 

passed over and the evolu- 
tion of the central organs 
will be briefly sketched. 

The nerve cells of the 
hydra are scattered diffusely 
throughout the body wall ; 
there is no special part of 
the body in which the cen- 
tral cells are massed. The 
higher animals all have a 
more or less highly cen- 
tralized nervous system. A 
simple type of centralization 
is seen in the starfish. 
Fig. 5 shows the general 

FlG. 5. Outline of a starfish, and nerv- 
ous system of the same 

Each arm of the starfish is supplied with outline of this animal's body 

a series of nerve cells indicated by the , , j- , i_ , r ,1 

lines passing through the various arms. *nd the distribution of the 

From these nerve cells, fibers extend to central nerVOUS Cells. Each 

the surface and receive sensory impulses , , 1 ,. 

and send out motor impulses. (After Loeb) double line represents a 

group of cells. It will be 

seen that there is for each arm a central group of cells, to 
which sensory excitations come from the surface of the body 
and from which motor impulses go out to the muscles. 
There is also a central ring which binds together the differ- 
ent arms and centralizes in a still higher degree the whole 
animal. This ring is in the neighborhood of the mouth 
opening, and its function is undoubtedly that of controlling 
the whole animal in taking food. 


Another type of centralization appears in any one of the 
segmented animals, such as an insect. Fig. 6 shows such a 
centralized nervous system. Each segment has its group of 
central cells, and all the segmental centers are related by 
connecting fibers to one another and to the highly developed 
group of cells in the first segments, 
which are near the mouth opening. 

Coordinating center of the body. 
The development of a complex cen- 
tral nervous system is of the high- 
est importance in animal life. As 
we have seen, the^ body cells of 
the higher animals are specialized. 
There must be some central con- 
trolling group of cells or the body 
would not be able to carry on its 
manifold functions in a unified and 
harmonious fashion. The central 
nervous system is the controlling 
and unifying organ. The arms of 
the starfish are made to serve the 
mouth because the mouth ring of 
nerve cells is the dominating organ 
of the body. In the beetle all the 
organs of locomotion are made to 
serve the head, which is both the 
entrance to the alimentary canal and 
the seat of the important special 
organs of sense, namely, the eyes and the feelers. The 
central nervous system reproduces in outline the whole body 
and is a connecting tract through which stimulations are 
carried from one organ to the other. 

It is hardly necessary to reiterate the statement made above 
that this evolution of nervous structures is paralleled by jn 
evolution in behavior. The number of acts of which an insect 

FIG. 6. A stag beetle, show- 
ing the outline of the body 
and the distribution of the 
nerve cells and fibers 

Each segment of the body has 
a ganglion of cells G, G, (/, 
from which fibers /% /?, F are 
distributed to the surface of 
the body for the reception of 
stimulations and the distribu- 
tion of motor impulses. The 
ganglion in the front section 
of the body is double and of 
greater importance than those 
in the posterior segments 


is capable, the complexity of its methods of locomotion, of 
protection, and of reproduction, all attest the intimacy of 
the relation between nervous structure and behavior. 

Complex paths within the nervous system. Not only so, 
but the central group of nerve cells begins to have certain 
internal paths which take on the largest significance for the 
animal's life. The energy which comes in at the sense 
organ of a beetle sets up through the central nervous system 
a most complex chain of acts. Think, for example, of such 
an insect aroused by the smell of food. It first flies to the 
spot, guided by the increasing intensity of the odor ; it lights 
on the food and then seizes it. In such a series of acts 
the nervous system has acted in the most complicated way to 
control and keep in action the various muscles of the body 
in the interests of the whole organism which is dependent 
for its life on its ability to find food and absorb it. 

Such considerations lead us to think of the nervous system 
itself as a complex organ made up of dominant centers and 
secondary centers with paths running between them. Our 
later study will fully justify such a conception. 

When the nervous system reaches this stage of organiza- 
tion, many of its inner paths and centers are determined by 
the animal's inheritance. Just as a starfish inherits arms and 
a mouth from its race, and a beetle inherits legs and wings, 
so each animal inherits certain paths through its central 
nervous system. These inherited paths play a large gait in 
controlling the life of the individual animal. The insect takes 
a certain type of food because its inherited sensory cells 
respond in a certain definite way to certain odors. Other 
special activities, such as depositing eggs and special modes 
of flight designed to carry the animal away from enemies, 
are due also to the organized tracts which run through the 
nervous system. Indeed, it appears in the study of insects 
and animals at the lower levels of evolution that practically all 
their modes of behavior are determined through inheritance. 


Experience comparable to the lower forms of human 
experience. If we try to guess what are the experiences of 
such an animal, we must not draw on our own experiences 
of meditation and deliberation. Deliberate casting about in 
thought for a course of action is far from characteristic of an 
insect. The analogy which we should borrow from human 
experience is the analogy of a fully organized habit or, better, 
the analogy of one of our own inherited modes of action, 
such as that exhibited in the winking of the eye or jerking 
the head aside when an object moves rapidly toward the face, 
threatening to strike it. Conscious experience is made up 
in such cases, not of clearly defined knowledge of the thing 
which gives rise to the experience, but rather of a vague 
excitement, followed by unrest when the instinctive winking 
or dodging does not adequately meet the requirements of 
the situation, and by satisfaction when the activity proves 

Differentiation of vertebrate central nervous system. 
Passing by long steps up the scale of life, we may next 
consider the nervous system of one of the lower vertebrates. 
Here we find that the centralized organization has gone be- 
yond that seen in the insects, but it is yet relatively simple. 
Fig. 7 shows the general form of the frog's nervous 
system looked at from above. In all of the vertebrates the 
nervous system is incased in the bones of the vertebral 
column and skull, so that the view here presented shows 
the appearance of the nervous organs after the bones and 
muscles and skin which cover these organs in the normal 
animal have been removed. The frog's nervous system may 
be roughly divided into two main sections. The first part 
lying behind the cerebellum consists of the long cylindrical 
spinal cord with the medulla, which is essentially an enlarge- 
ment at the upper end of the cord. The cord and medulla 
are directly connected with the surface of the body by means 
of a great number of fibers. The incoming sensory impulses 



from the skin are received through certain of these fibers, 
and motor impulses are distributed to the muscles through 

others. There .are many cells 
in the cord and medulla, their 
chief function being to form 
links of connection* between 
the incoming sensory fibers 
and the outgoing motor fibers. 
If the cord and medulla are 
separated from the higher cen- 
ters by a cut just below the 
cerebellum, the animal con- 
tinues to live and is capable 
of certain simple responses to 
sensory stimuli, the only depar- 
ture from the normal being that 
activities called out by stimuli 
show a machine-like regularity. 
Thus, if a drop of acid is 
applied to the skin of the frog's 
trunk, the nearest leg brushes 
off the excited spot. The acid 
sets up a sensory process ; this 
travels up to the cord and 
there passes through certain 
central cells and is sent back 
along motor fibers to the mus- 
cles. The whole process is 
like that described a few pages 
back as taking place in the 
hydra. There is no evidence 
that a frog having its spinal 
cord severed from the higher 
centers has any ability to carry on the higher processes of 
discriminating reaction which involve intelligence. 

FIG. 7. The nervous system of a 

frog as it would appear if the skin 

and muscles and protecting bone 

were removed 

A, spinal cord with some of the nerve 
fibers which extend from this organ 
to the surface of the body (in the 
posterior region a plexus of fibers 
extends to each of the posterior ex- 
tremities; in the anterior region, a 
plexus extends to each of the anterior 
extremities) ; B, medulla ; C, cerebel- 
lum: Z>, optic lobes, which are con- 
nected with the eyes by optic fibers that 
pass underneath the brain; E, optic 
thalami ; /? cerebral hemisphere. The 
anterior portions of the hemispheres 
constitute what are known as the olfac- 
tory lobes. These lobes are directly 
connected by means of the fibers shown 
in the figure with the olfactory region. 
Many of the nerve fibers which extend 
from the medulla to the surface of the 
body are omitted in this drawing 


If the frog is normal, that is, if the connection be- 
tween the spinal cord and the higher centers is intact, the 
impulses received by the cord, in addition to circulating 
through the lower centers, are carried up to the higher 
centers. Here they are influenced by the action of higher 

Two types of higher centers: first, higher sensory centers; 
second, indirect centers. The centers above the cord and 
medulla, ^hich constitute the higher group of structures in 
the frog's central nervous system, are of two kinds. First, 
there are certain sensory centers, namely, the large optic 
lobes and the olfactory lobes. These connect respectively 
with the eyes and nose of the frog and receive sensory 
impulses from these higher senses. The large size and 
forward position of these two centers indicate the impor- 
tance of the functions which they perform in the animal's 
life. Especially, the large size of the optic lobes is directly 
related to the fact that the frog uses its sense of sight in 
capturing the insects on which it subsists. Second, there 
are, as will be seen from an examination of the figure, 
certain parts of the upper brain which have no direct 
connection with the surface of the body. Thus there are 
large masses of tissue in the cerebrum and in the optic 
thalami which lie between the olfactory and optic centers. 
These are higher centers, where the processes which 
are received in the sensory centers may flow together 
and fuse into higher and more complex forms of nervous 

The meaning of these higher centers will be understood 
if we use an analogy. In a large business concern there are 
minor clerks and managers who attend to all the immediate 
details. These lower officers are in contact with the outer 
world. Far removed from such direct contact, in a quiet, 
central office is a central manager, to whom the minor offi- 
cers report when they need to bring other workers in the 


establishment into cooperation or when they have problems 
requiring greater deliberation and broader views than they 
can command. 

The indirect nervous centers are fusion centers or associa- 
tion centers, to which all the lower centers refer their activi- 
ties when these activities need a higher coordination. There 
is thus developed within the nervous system a higher level, 
which is of superior importance. 

Large indirect centers characteristic of highest animals. 
If we follow the evolution of the nervous system from the 
frog up to man, the most impressive fact is that these in- 
direct centers are the ones which show marked enlarge- 
ment. A study of Fig. 8 will bring out the facts. A, 
in the upper left-hand corner of this plate, shows the 
brain of a codfish. At the right is the cord, enlarging 
under the cerebellum into the medulla. The cerebellum is 
much more fully developed than in the case of the frog. 
This is one of the indirect centers referred to in the open- 
ing sentence of this paragraph. The midbrain, which is 
the optical center, is very large, and at the extreme left 
the olfactory region can be seen. The cerebrum consists 
in this case solely of the corpus striatum, an organ which 
in the higher brains is subordinated to the cortex of the 

B, in the plate, needs no special discussion. The in- 
crease in relative importance of the cerebrum is unmistak- 
able. In C the preponderance of the indirect centers is 
even more evident. The surface of the cerebellum is folded 
so as to make more room at the surface of this organ for 
the nerve cells. 

Finally, D shows the final type of brain which is char- 
acteristic of the highest animals. The cerebrum literally 
covers all the forward organs. It is folded or convoluted on 
its surface for the same reason as the cerebellum. The 
cord, medulla, and other lower organs are present and, 







**> c 
o g 
a g 

be , 

3 ; 


<u rS 

bfl ^ 


CO g 

2 & 

considering the size of the animal's body, are organs of about 
the same importance as in the frog or codfish. The cerebrum 
and, to a less extent, the cerebellum are the organs which 
attract attention. The higher functions of the dog both in 
behavior and in the realm of intelligence must be related to 


the enormous development of his cerebrum. It is in the 
indirect centers of the cerebrum that those nervous processes 
take place which condition intelligence and the correspond- 
ing types of behavior. In the lower animals a sensory im- 
pulse passes very directly through a relatively small amount 
of central tissue to the organs of action. In these lower 
animals, also, most of the paths of transmission are in- 
herited. In the higher forms, on the other hand, there is a 
vast amount of tissue, and the sensory impulse may be greatly 
modified by traveling along a complicated route before it is 
discharged into the muscles. In the course of this long 
journey it may be united with many sensory impulses from 
other sources, so that the final action is the resultant of 
many cooperating impulses. 

Traces of past impressions also present. Not only so, 
but this complex tissue becomes a storehouse for a great 
variety of changes in structure which result from the recep- 
tion of sensory impressions and the sending out of motor 
impulses. The phrase "tablets of memory" begins to take 
on a very vivid meaning to the student of brain anatomy. 
Here in the central masses of tissue to which the rest of 
the nervous system reports are the real seats of organized 
personal life, the records of which are deposited in the 
course of experience. 

Meaning of evolution of complex organisms. The pro- 
found significance of this increasing inner complexity of the 
nervous system can be understood only when we recognize 
that increased inner complexity has always been the outcome 
of animal evolution in every organ and every function. 

Let us study, for example, the evolution of those organs 
of the body that produce the temperature which is charac- 
teristic of the higher, so-called warm-blooded, animals. The 
simple organism is without the power of generating a con- 
stant inner temperature and is therefore utterly dependent 
for its body temperature on the environment. As a result, 


such an animal cannot carry on vigorous life in the cold. 
The complex organism, on the other hand, has purchased 
self-sufficiency in matters of temperature by the evolution 
of a complex set of temperature-producing organs. The 
range of such an organism's life is consequently enormously 

Another striking example of increasing self-sufficiency is 
furnished by studies of the reproductive processes. In the 
simple forms of life the offspring is exposed very early to 
the mercies of the environment. The parent organism has 
no adequate means of protecting the young. Gradually the 
parent grows more complex and in the same degree better 
able to protect the offspring. There is an increase in the 
food supply deposited with the egg and an increase in pro- 
tective devices. The goal of this line of evolution is reached 
when the parent becomes sufficiently complex in structure 
to provide for the elaborate development of the offspring 
within the parent organism. The whole process of evolution 
is here seen to lead in the direction of self-sufficiency on 
the part of the organism. Instead of depending on the 
chances of environmental conditions, the organism builds 
up an environment of its own within which its reproductive 
processes may be brought to a high degree of completion 
before exposing the product to the external world. 

Every organ of the complex animal bears witness to the 
truth that inner self-sufficiency is the end toward which 
organic evolution has been progressing. There are organs 
for the storing of energy, so that the individual shall be 
relatively free from the necessity of securing immediate 
nutrition. There are organs for the secretions of chemical 
reagents which shall convert the raw material used as food 
into proper ingredients for the building up of body tissues. 
Organisms have always exhibited in their higher forms 
organs of mobility, which make them frefe to move at their 
own initiative. 


In all these cases the obvious significance of increasing 
complexity is increasing autonomy of the individual. The 
process of evolution has resulted in a more stable set of 
inner conditions, which make it possible for the vital proc- 
esses to go on without interruption or hazard from fluctua- 
tions in the outer world. 

Inner organization essential to highest forms of personal 
behavior. The meaning of a complex nervous system thus 
becomes clear. Nature is evolving an organism in which 
inner processes are to be of prime importance. Impressions 
must be received from the outer world, but the important 
question now is, What will be done with these impressions 
in the inner nervous system, where the impression is distrib- 
uted and combined with other impressions and with traces 
of past impressions ? 

We are thus brought to the point where we realize the 
meaning of the sharp antithesis between inner personality 
and sensory impressions. Two men receive the same im- 
pression ; to one it means much, to the other little. The 
reason for the difference is that in one case there is a highly 
organized central response, in the other there is no such 

Our later chapters will have much to say about the inner 
organization of the nervous system. In the meantime, it 
should be kept in mind that behavior runs parallel with this 
highest evolution. Man is not only complex in his inner 
nervous life, but he is complex in his acts. When one 
thinks of the complexity of speech or of the forms of skill 
exhibited in the arts, one realizes that behavior and nervous 
organization go hand in hand at the highest levels of life 
as well as at the lower levels, which were studied in the 
opening paragraphs of this chapter. 

Characteristics of behavior of higher animals. The pur- 
poses of our present discussion will be best served, there- 
fore, by reviewing briefly some of the characteristics of the 


behavior of the higher animals. First, the variety of move- 
ments is vastly increased. Up to a certain point in animal 
evolution the number of organs of movement, of limbs and 
oral muscles for example, increases to meet the increasing 
needs of the animal ; but ultimately a point is reached where 
development of movement goes forward without any corre- 
sponding development of new limbs or muscles. This later 
stage is characterized by the development of nervous struc- 
tures which make it possible to use the given muscles in a 
greater variety of combinations. Thus a skilled artisan de- 
pends for his perfected movements, not on the development 
of new arm muscles or finger muscles, but on the develop- 
ment of finer coordinations of those muscles which all human 
beings possess. 

A second striking fact of behavior which parallels the 
development of complex nervous centers is that slight stim- 
uli may set up the most elaborate processes. The value of 
the stimulus in such a case is determined not by the in- 
tensity or quality which it has in itself but by the complex 
organization which it arouses to action. Conversely, a strong 
stimulus may be absorbed in the elaborate organization and 
produce no immediate effect. These statements can be illus- 
trated by the behavior of a frog under the two kinds of 
conditions discussed above, namely, when the animal has 
been deprived of its higher centers and when its nervous 
system is intact. If a stimulus is applied under the former 
and simpler conditions, a response will follow immediately 
with mechanical regularity. This response will be of a very 
simple and direct type, usually consisting in a movement of 
one of the legs up to the point of irritation. In a second 
case we may apply the same stimulus to- a~frog in which the 
cord and medulla are connected with the higher centers. 
The reaction in this case will be of an entirely different 
character. It will usually not come immediately, and its 
form will depend on a great variety of .complex conditions. 


Thus, the frog may jump away, it may croak, or there may be 
a complete absence of apparent reaction. If such results as 
these appear in so simple an animal as a frog, the complexity 
of possible organization in a human being can be imagined. 
Third, as perhaps the most important result of the de- 
velopment of indirect nervous centers, is the fact that the 
impressions and activities which appear in the course of 
individual life are stored up and enter very largely into 
the determination of nervous organization. As pointed out 
above, the lower direct centers are in the main determined 
in structure by heredity ; the higher centers, on the other 
hand, are found to be undeveloped at birth, so that the 
stimuli which act upon the individual find at the beginning 
of life a mass of undeveloped tracts through which they 
may be transmitted. It has long been recognized that the 
infancy of all the higher animals, especially human infancy, 
is very much longer than the infancy of the .lower forms. 
The reason for this appears as soon as we recognize that 
the higher centers of the nervous system are not maprjfed 
out by heredity and require time to mature. 


The statements which have been made throughout the chapter 
may be summarized in a table. This table shows the steady growth 
in the complexity of animal structure and animal behavior and 
opens the way for an understanding of the place of consciousness 
in the economy of life. 







Very simple 


Most complex 



cells diffused 
through wall 
6f body 

and central- 

by the great 
of indirect 







of Sense 


Very little, if 
indeed at all, 


Further dif- 
reaching com- 
plete differen- 
tiation (see 
later chapter) 



a, limited in 


a, increasing 
in variety 
as compared 
with unicellu- 
lar forms 

Grows more 
and more 
a, shows va- 
riety of in- 
stinctive acts 

Most complex 

a, specialized 
movements of 
great variety 

, made up of 
single acts 

b, made up of 
simple series 

6, made up of 
of factors 

b, long coordi- 
nated trains 

c, very little 
modified by 

<:, very little 
modified by 

<r, somewhat 
modified by 

<r, guided 
chiefly by 

</, follows 
very directly 
on stimulus 

</, direct* as in 

</, for the 
most part 
direct, but in 
higher forms 
includes indi- 
rect or mem- 
ory factors 

//, chiefly indi- 
rect, as shown 
in man in such 
activity as 

Type of 

like vague 

Vague feel- 

Possibly vague 
recognition of 
those objects 
which call for 
instinctive re- 
actions, but 
chiefly affec- 
tive ; that is, 
made up of 

and feelings 
present, but 
overlaid by 



External plan like that of all vertebrates. The structural 
plan of the human nervous system is the same as that of all 
vertebrates. Fig. 9 shows the out- 
lines of the whole system. Through 
the vertebral column runs the cord. 
This enlarges at the upper end into 
the medulla. These two organs are, 
in proportion to the size of the body, 
about the same in all vertebrates. 
Above the medulla can be seen only 
the cerebellum and 'the cerebrum. 
The parts corresponding to the optic 
lobes and other minor centers of the 
upper brain are wholly covered by 
the enormous cerebrum. The sig- 
nificance of this development of the 
cerebrum and cerebellum has been 
indicated in the foregoing chapter. 
General plan of the minute nerv- 
ous structure as related to conscious- 
ness. The inner structure of this 
nervous system is of importance to 
the student of conscious processes. 
It is, to be sure, impossible to trace 
with the microscope the inner struc- 
tures which are set in action when 
any given mental process takes place. 
For example, when one sees the letters of a printed page, there 


FIG. 9. General form and 

position of central nervous 




must be parts of the nervous system which are aroused, but we 
cannot trace the exact paths along which travels the nervous 
energy. We can trace the general plan of inner organization. 



We can see the broad avenues, but 
must infer most of the details. The 
problem presented to the student of 
psychology is not unlike the problem 
of planning a journey with a map. 
One sees where there is a passage and 
where one cannot go. Sometimes the 
map is not complete. But in many 
cases the map gives a general view 
of the journey and some idea of its 
probable details. 

The nerve cell and its parts. The 
study of inner organization must begin 
with a description of the elements out 
of which the nervous system is made. 
The elements are cells of a highly 
specialized structure. These cells are 
called neurones. Each one is made 
up of a nucleus, a cell body of proto- 
plasmic tissue surrounding the nucleus, 
and a series of processes extending 
from the cell body. The processes 
are of two kinds ; namely, dendrites, 
or branching arms, which usually con- 
duct impulses toward the cell body, 
and a single long nerve fiber which 
carries the impulse outward from the 
cell body. Fig. 10 shows two neurones with all their charac- 
teristic parts. It will be noted that the long fiber is made up 
of several parts. There is a sheath around most of the long 
fibers of the nervous system. This is not an essential part 
of the nervous structure, but an external protecting structure. 

Two nerve cells 

Two nerve cells, A and /?, 
are here represented with 
their axones C and D. C ex- 
tends from the cell to a mus- 
cle ; shortly after leaving the 
cell the axone is surrounded 
by a heavy protecting sheath, 
as indicated in the figure, 
and known as the medullary 
sheath. At XX there ap- 
pears an outer sheath, known 
as the Sheath of Schwann. 
The medullary sheath ends 
at the point where the fiber 
divides into a fine network 
and passes into the muscle. 
The axone D communicates 
with another cell. (After 


The neurones are organized into chains. An impulse 
acting on one cell is transmitted to other connected neurones 

until, finally, the impulse 
reaches a cell connected 
with a muscle fiber. The 
contact between neurones 
in the higher nervous sys- 
tems is indirect, as shown 
in Fig. 1 1 ; that is, the fiber 
from one cell does not pass 
directly into another cell, but 
breaks up into a fine net- 
work of fibrils and inter- 
laces with the dendrites from 
other cells. The connections 
of a single cell may be very 
numerous by virtue of the 
branching of the dendrites 
and because of the indirect 
relations between neurones. 
The point of relation be- 
tween two neurones is known 
as a synapse. At the syn- 
apses, impulses are redistrib- 
uted in the greatest possible 
variety of directions. 

Complexity of structure 
related to forms of action. 
An examination of neurones 
various animals and at 

FIG. ii. A number of different types 

of connection between nerve fibers 

and cells 

A and A' represent incoming sensory 
fibers which bring stimulations from 
different directions to the cell B. All of 
the stimulations acting upon B are trans- 
mitted along the fiber C, and at the end 
of this fiber may affect various cells, such 
as D and E. From the cells D and B 
the stimulations may pass in different 
directions, as indicated by the arrows. 
The stimulations from A and A' fuse in 
the cell B. The stimulation from the cell 
B is subdivided and redistributed from 
D and E. All connections are indirect 
or synaptic 


different stages of individual 
development shows clearly 
that the number of branches 
of the cell is an important factor in determining the com- 
plexity of the nervous organization into which the neurones 


may enter. Fig. 12 shows the increasing complexity of 
neurones as we ascend the scale of animal life, and also 
the increasing complexity of neurones of a single human 
being as the nervous structures mature. The lesson to be 
learned from these two series 
of figures is clear. The com- 
plexity of a cell and the number 
of systems of connections into 
which the cell may enter in- 
crease in direct proportion to 
each other. 

Synapses as paths of organi- 
zation. Whether they are units 
in one of the lower centers 
of the nervous system or 
in a higher center, the cells 
are always connected through 
synapses and always transmit 
impulses indirectly, thus com- 
bining them and distributing 
and redistributing them. JThe 
nervous system has been com- 
pared to a telephone switch- 
board. The senses send in 
excitations and the central 
cells send these to the various 
muscles of the body. On the 
way to the muscles one set 
of sensory excitations unites 

with another set from some second organ of sense. The 
combinations and distributions are somewhat like those of 
the switchboard, only infinitely more complex. How com- 
plex they are, one can imagine from the statement that 
the total number of cells in the human nervous system 
has been estimated as somewhat more than i2,ocxD,ooo,cxx). 

FIG. 12. The development in com- 
plexity of nerve cells in the course 
of animal evolution and in the 
course of the development of a 
single individual 

A is the nerve cell of a frog; /?, a 
lizard ; C, a rat ; ZP, man. The possi- 
bility of developing definite paths 
between various neurones increases 
in proportion to the increase in the 
number and complexity of the den- 
drites from the cells, a is a neuroblast 
without dendrites, from the earlier 
embryonic development of a human 
brain, b shows the beginnings of den- 
drites at the upper end of the cell. 
In c, in </, and in e the dendrites 
increase. The form of the mature cell 
can be seen by referring to D in the 
upper series. (After Cajal) 


Paths in spinal cord. Let us follow a sensory impulse 
through the lower paths of connection in the spinal cord. 
Fig. 13 shows a magnified section across the cord. The 
left side of the figure shows the appearance of the section 
as seen under the microscope, while the right side is dia- 
grammatic and allows one to trace some of the paths 
through the tissue. The figure shows that the cord is 
bilateral ; that is, made up of two similar parts, one for 
each side of the body. The nervous system throughout is 

FIG. 13. Transverse section across the spinal cord 

bilateral, just as are the nostrils and eyes and arms. In the 
middle of the cord is a mass of cells. They have a gray 
:olor and are called, collectively, gray matter. Around the 
mass of cells are bundles of fibers which, because of their 
glistening white color, are clearly distinguishable from the 
:ells. Some fibers are seen running into the cord and out 
rf it at the level of the section ; some are running back 
and forth within the cord ; the majority appear as mere 
spots because they run in a direction perpendicular to the 
plane of this section and are cut squarely across in making 
the section. 


On the right side of the figure at A is seen a nerve 
trunk, or cable-like bundle made up of many nerve fibers. 
This bundle of fibers breaks up into two roots ; the root P 
is a sensory root along which sensory impulses enter the 
cord ; the root M is a motor root along which impulses 
leave the cord on their way to the muscles. At G is a 
group of cells outside the cord, constituting an independent 
ganglion. These are the cells which send their fibers to the 
skin and receive the impression of touch. If one has the 
patience to trace the fibers i, 2, 3, and 4, one will find 
typical paths across the cord. This diagram alone is not 
adequate, however, for many of the fibers must be shown in 
a flat section of this kind as abruptly broken off. They 
pass in reality out of the level of this section. Fig. 14 is 
therefore added to give an idea of the way in which the 
various levels of the cord are related to each other and 
to the cerebrum. B represents a section of the spinal 
cord ; A, a portion of the cerebral cortex. D l represents 
a region of the skin in which the sensory ending of a 
tactual fiber from the cell D is distributed. A pressure 
stimulation acting upon D 1 will excite the nerve cell and 
send a stimulation inward, as indicated by the arrows. 
This stimulation will pass upward and downward to various 
levels of the cord, as indicated by the branching of the 
incoming fiber at e. Certain portions of this incoming stim- 
ulation will be distributed through the spinal cord at differ- 
ent levels, as indicated by the small collateral branches 
passing horizontally out of the branches of the sensory 
fiber (see also Fig. 13). At /the incoming fiber communi- 
cates with a nerve cell which, in turn, connects with the 
cerebrum. This diagram is much too simple, more than 
one cell being necessary for the transmission of this stimu- 
lation to the higher centers. When the stimulus reaches g 
in the cerebral cortex, it acts upon the large cell there shown, 
and is transformed into a motor impulse. It then passes 



downward along the fiber a, which gives off horizontal 
collaterals at different levels of the cord. Through one of 
these collaterals or through the termination of the centrif- 
ugal fiber, as indicated at b > the stimulus is transmitted to 

a motor cell in the 
spinal cord, and 
from this cell is 
carried outward to 
the muscles indi- 
cated at C. 

Reflex tracts. 
When a sensory 
stimulation passes 
through the cord 
and comes out in 
an immediate reac- 
tion, the process 
is called a reflex. 
Thus, when one 
touches a hot iron 
and jerks back the 
hand, such a proc- 
ess is exhibited. 
The nerve cells in 
the cord are in this 
FIG. 14. A diagram to illustrate the course of the fashion in control 
sensory stimulation when it passes upward from r manv o f U e 
the level of the spinal cord at which it is received. ^ 

(After Cajal) simplest forms of 

behavior, such as 

the organic processes involved in digestion, and the simpler 
protective movements, such as the withdrawing of the 
hand above referred to. The nerve cells of the cord are 
larger than in other parts of the system, hence do not 
fatigue as readily ; they watch over the body when the cells 
in the higher centers are asleep. 



Transmission to higher centers. In addition to serving 
as a seat for the reflex centers, the cord is a communicating 
cable, as was shown in Fig. 14, carrying up to the brain 
messages from the surface of the body and carrying back 
messages to the muscles. 

All nervous organs in part inde- 
pendent centers. The higher nervous 
centers above the cord are more 
elaborate organs, but they are in 
essential structure the same as the 
cord. Below the cerebrum every 
organ of the nervous system may be 
said to consist, like the cord, of a 
combination of relatively independent 
cell centers and transmitting tracts. 
In the cerebrum the whole surface 
of the organ is made up of inde- 
pendent cell centers. 

Cerebellum. In the cerebellum the 
central function predominates. This 
can be shown by examining a section 
of this organ. Fig. 15 shows one of 
the lamellae, or folds of the cere- 
bellum, much enlarged. It will be 
seen from this section that the cells 
lie, not in the center of the organ as 
in the spinal cord, but at the outer 
surface. Fibers enter the cerebellum in bundles and termi- 
nate 'in a fine network of fibrils about the cells which are 
situated on the surface. The surface, which is technically 
known as the cortex, is increased very greatly in extent by 
the folding, which can be seen in any figure representing 
this organ. The result of the folding is that provision is 
made for an enormous number of cells in a relatively 
small cubical space. Through the action of the cells in 

FIG. 15. A diagrammatic 

section through a part of 

one of the folds in the 


A fiber, a, entering from 
some other part of the cen- 
tral nervous system, distrib- 
utes its impulse to the small 
cells c and to the larger 
cell b. From 6, the stimu- 
lus is carried outward along 
the descending fiber, d also 
shows the termination of an 
incoming fiber. The organs 
here figured serve to redis- 
tribute impulses from other 
parts of the nervous system. 
(After Cajal) 

4 6 


the cerebellar cortex, an impulse which comes into the 
cerebellum as a single impulse from one of the higher 
centers, as, for example, from the cerebrum, may be sub- 
divided into a great number of currents so as to arouse, 



Corpus Callosum 


FIG. 1 6. The brain seen from below and cut open to show the paths of 
fibers from the cortex of the cerebrum to the lower organs 

In the lower part of the figure near the middle is the medulla. One side of the 
cerebellum is shown on the left. Sections of the cerebral cortex constitute the chief 
part of the figure, especially at the left above and below. From the cortex peduncular 
fibers pass downward. Near the top of the figure the heavy band of fibers constituting 
the corpus callosum crosses from one hemisphere to the other. (After Edinger) 

when distributed to the active organs, a whole system of 
muscles. Indeed, there is evidence that the cells of the 
cerebellum contribute in the way indicated to muscular 
coordinations in all parts of the body. 


Cerebrum and its systems of fibers. From the cord and 
cerebellum and the other minor centers of the nervous sys- 
tem we turn to the cerebrum. Our study of the evolution 
of the nervous system showed the dominating importance 
of this organ in all of the higher animals. The cerebrum 
is a complex organ to which sensory impulses come from 
all parts of the body and from which motor impulses are 
sent out to all the voluntary muscles. It is not directly 

FIG. 17. Sketch showing some of the association fibers connecting various 
parts of the cortex of the cerebrum with one another. (After Edinger) 

connected with the surface of the body, but is indirectly 
the organ in control of all parts of the body. It is a cen- 
tral clearing house for the organism. It is the part of the 
body most intimately related to consciousness. 

In structure the cerebrum consists of an external folded 
or convoluted layer of cells known as the cortex. This cor- 
tex is from one eighth to one twelfth of an inch in thick- 
ness and shows many variations in structure in its different 
parts. To these variations in the structure of the cortex 

4 8 


further reference will be made later. The central mass of 
the cerebrum is composed of fibers which provide for the 
connection of each point of the cerebral cortex with every 
other part of the nervous system. The general structure of 
the cerebrum may, perhaps, be comprehended most easily 
by referring to the systems of cerebral fibers. There are 

three types or systems of 

First, there are great 
bundles of fibers connect- 
ing the cerebrum with the 
lower centers and constitut- 
ing the paths along which 
motor impulses descend. 
These constitute the pe- 
duncular tract. Some of 
these fibers were shown 
in the diagram illustrating 

FIG. 1 8. A transverse section across the 
two hemispheres in a plane passing verti- 
cally through the cheek bones parallel 
to a line connecting the two ears 

This section shows the fibers which establish 

communication between the two hemispheres, shown in Fig. I/, which 

When the fibers in this figure are supple- connect the different points 

of the cortex of one hemi- 
sphere with other points 
in the same hemisphere. 
These fibers are techni- 
cally known as association fibers. The third bundle of fibers 
extends from one hemisphere of the cerebrum to the other 
hemisphere. The fibers of this group are known as the 
commissural fibers, and go to make up the corpus callosum, 
or bridge of fibers, conspicuous in any median section of 
the cerebrum and shown in Fig. 18. This bridge was also 
shown in Fig. 16. 

the paths in the spinal 
cord (Fig. 14) ; the whole 
system is shown in Fig. 16. 
Second, there are fibers, as 

mented by those represented in the two 
preceding figures, it will be seen that every 
point on the cortex of the cerebrum is in 
communication with all other parts of the 
nervous system. (After Edinger) 



Structure of cerebrum as indicating way in which impulses 
are organized. No clearer evidence of the function of the 
cerebrum can be found than that which is given in the 
structure of its systems of fibers. An impulse which reaches 
the cells of the cerebral cortex through the sensory, or 
incoming, fibers of the peduncular tract is brought to the 
cortex for the purposes of redistribution and combination 
with other impulses. The elaborate system of interconnect- 
ing tracts provides for infinite recombinations of nervous 

FIG. 19. Two sections representing portions of the cerebral cortex from 
two areas of the human brain 

On the left there are shown the sixth and seventh layers of the visual center. The 
horizontal distribution of the dend rites of the large pyramidal cells is characteristic 
of this region. On the right is a part of the motor center, showing giant pyramidal 
cells which in size and distribution of dendrites differ from those in other centers. 

(After Cajal) 

impulses. We shall refer in all of our later discussions to 
the organization of nervous processes which goes on in the 
cerebrum. The term "organization," so used, refers to the 
fact that a nervous impulse, when it reaches the cerebrum, 
is united with other impulses and is carried along complex 
series of paths, until finally it is discharged into the motor 
channels which pass outward to the muscles. No impulse 
which reaches the cerebrum can escape combination with 
other impulses; the purpose of the whole structure is to 
provide channels for the most complete interrelating of all 
the higher nervous processes. 


Cerebral cortex complex. The cortex of the cerebrum 
has a structure of such complexity that it has been impos- 
sible, until very recently, to define with 
anything like certainty its various parts. 
Fig. 19 represents two typically different 
areas. An examination of these dia- 
grams shows that the cells are of differ- 
ent types and the mode of interlacing 
of their dendrites is different. Fig. 20 
shows a diagrammatic representation of 
some of the different elements which 
are characteristic of the cerebrum. By 
means of this figure the cells and fibers 
which in reality are interlaced can be 
distinguished from each other. 

Localization of functions. Though we 
are ignorant of the meaning of many of 
the details of cortical structure, we are 
well informed as to the functions of 
many areas of the cortex. The cortex 
may be divided into three kinds of areas 
or centers ; these are sensory areas, 
motor areas, and association areas. The 
sensory areas are those which have the 
most direct relations to the various 

those which stand in most direct rela- 
tions to the active organs. There is no 
quateiy the complexity of part of the cerebrum which has simple 
cenfar^not' here^re! anc * immediate relations to the surface 
sented. A general impres- of the body, so that the terms "sensory" 

gain^d^rthe figure o'f and " mOt r " are merd Y relativC tei S > 

the complexity of the cor- the sensory centers being those points 

i stimulations from the organs 

FIG. 20. A diagram- 
matic section showing 
the structure of the 
cortex of the cerebrum 

On the left-hand side of 
the figure the cells alone 
are shown. On the right- 
hand side of the figure 
the fiber systems alone 

tex. (After Edinger) 

of sense are first received in the cerebrum, the motor areas 


being those points from which the stimulations pass out of 
the cerebrum on their way to the muscles. The association 
areas, as the name indicates, are areas of a still more indi- 
rect character, in which sensory impulses, after being received 
in the sensory areas, are recombined and redistributed. In a 
very proper sense of the term, all cerebral areas are associ- 
ative areas, for they all serve the function of indirect com- 
bination and distribution of nervous impulses. Those which 
are specifically designated as associative have claim to the 
specific name because they perform a function of even higher 
combination than do the others. Figs. 21 and 22 show the 
centers of these types which appear on the surfaces of the 
human cerebrum. 

Stimulation the first method of discovering cerebral locali- 
zation. It may be interesting to digress for a moment from 
the structure of the cortical centers for a discussion of the 
methods by which these centers have been located. A great 
number of experiments have been tried on the higher 
animals. Certain of the areas have been artificially stimulated, 
and when muscles in different parts of the body have 
responded promptly and regularly to these stimulations, the 
connection between the areas stimulated and the muscles 
thrown into action has been recorded. Evidently, artificial 
stimulations of this kind would be of little value in locating 
sensory or association areas, for there are no clearly marked 
muscular effects when the stimulus is applied to areas other 
than those directly related to the muscles. For example, 
the stimulation of the visual center would show only the 
motor effects of such stimulation and would not give any 
clear indication of the sensory character of the area. 

Extirpation and comparison of pathological cases. A sec- 
ond type of experiment which has been productive of results 
depends upon extirpation of the tissues. Certain areas of the 
cerebral cortex of animals are cut or burned out, and the loss 
in function resulting from this removal of the nervous tissue 


is carefully studied. This method can be used in locating 
both sensory and motor centers. There are cases of disease 
of the human nervous system analogous to these cases of 

FIG. 21. The outline of the lateral surface of the cerebrum with the typical 
convolutions, as given by Flechsig 

The shaded portions indicating the sensory and motor centers, and the small circles 
indicating certain well-defined association areas, are given according to Tschermak 
in Nagel's " Handbuch der Physiologic des Menchen." Vertical lines in the shaded 
areas indicate motor areas; horizontal lines indicate sensory areas; oblique lines 
indicate sensory-motor areas. /, /, /, /, / are the motor areas for the toes and 
foot ; 2, 2, 2 are the motor areas for the shoulder, elbow, and wrist ; j, j, j, j are 
the areas for the fingers and thumbs; 4, 4, 4, 4 are the motor areas for the eye 
and other parts of the face ; j is the center for the vocal cords ; 6, for the tongue ; 
7 is the sensory area for the head ; 5, 8, 8, 8 are the sensory areas for the regions 
to which motor stimulations are distributed by the areas i-b ; 9, 9 are the sensory- 
motor areas of the trunk ; //, visual area and occipital area for the eye movements ; 
72, auditory area and temporal center for visual fixation ; /j, olfactory bulb ; 74, 
probably olfactory area. The area where vertical and horizontal lines cross between 
the motor areas 1-6 and the sensory areas 7, 8 is probably connected with the 
muscle sense. A^ motor writing center ; B, Broca's motor speech center ; C, prob- 
ably memory-motor speech center ; Z>, sensory music center ; E, Wernicke's sensory 
speech center ; F, memory-sensory speech center ; G, memory reading center ; //, 
sensory reading center. All of these lettered areas are associational centers 

extirpation in animals, and careful study of the loss of 
human functions shows that the human cortex is subdivided 
in much the same way as that of the higher mammals. 



Embryological methods. There are other methods of 
investigating cerebral areas which deal with the internal 
structures. One of the most productive of these methods 
depends upon the fact that the different areas of the cere- 
brum do not develop at exactly the same period in the 
embryological or infant life of a human being. The human 



FIG. 22. The median surface of the human cerebrum showing, as in Fig. 21, 
the various areas 

8, sensory area for the lower extremities ; <?, 9, sensory-motor areas for the trunk ; 
/o, motor area of the lower extremities ; //, visual area and occipital motor area for 
visual fixation ; /j, olfactory bulb ; 14, probably olfactory area ; /j, /j, /j, /j, olfactory 
areas ; /6, /6, probably gustatory areas. (For reference to authorities for this figure, 

see Fig. 21) 

embryo exhibits in its early stages a development of the 
nervous system about the central fold or fissure, known as 
the fissure of Rolando. This area of earliest development 
is in the region marked in Fig. 21 as the motor area and 
the area of tactual sensitivity. Later, the nervous system 
matures in the remaining sensory centers in such sequence 
that it is possible, by the study of the microscopic anatomy, 
to secure a fairly complete chronological account of the 


development of the different regions. The association areas 
are the latest to develop. Indeed, in the association areas 
the development can be traced for a period after birth, and 
indirect evidence seems to make it clear that the development 
goes forward well on into mature life. 

Association areas. The visual area in the occipital region, 
as indicated in Figs. 21 and 22, is the area through which 
impulses resulting from retinal stimulation are first intro- 
duced into the cerebrum. A similar area for the reception 
of auditory impulses appears, as indicated in Fig. 21, just 
below the Sylvian fissure. Without entering further into a 
discussion of the various centers, it will be enough to call 
attention to the relation between the visual and auditory 
areas and the association area lying between them. The 
association area in question, known as the parietal associa- 
tion area, has developed in the course of the evolution of 
the cerebrum between the visual and the auditory centers as 
the area in which the stimulations from these two centers 
may be brought together and combined. There are many 
evidences that the combinations of visual and auditory im- 
pulses do, as a matter of fact, go on in the parietal associa- 
tion center. For example, there is in this parietal region 
one area which is of great importance in the function of 
speech. If this association area involved in speech is dis- 
turbed, the individual may remain quite capable of receiving 
visual impressions through his eyes and of receiving audi- 
tory impressions through his ears. He may even be capable 
of articulation, which is a motor function, but he will lack 
the ability to interpret the impressions which he receives 
when he hears or sees words or to give expression to a 
coherent series of ideas. The area in question has there- 
fore been designated as the ideational area. It is ideational 
rather than sensory, because it is the seat of a series of 
functions more elaborate than those which are involved in 
the m*ere reception of impressions. It is the center for the 


combination of visual or auditory impressions. More than 
this, the association area is a center which becomes more 
and more highly organized in its inner structures through 
use, so that its influence on any present impulses is, doubt- 
less, such that we are justified in saying that it adds to 
these impulses the effects of past experience. In an im- 
portant sense it associates present impressions with past 
impressions, as well as combines present impressions from 
different senses. It thus serves in a large way the function 
of a reorganizing center for visual and auditory impressions. 
Significance of the central position of the general motor 
area. Another important fact, which will be observed im- 
mediately on the inspection of Figs. 21 and 22, is that the 
general motor area occupies a relatively central position in 
the cerebrum. Around the motor area are a group of asso- 
ciation areas where impulses are united on their way to 
motor discharge. The area of touch and of general sensi- 
bility seems to offer an exception to the general rule of 
distribution of sensory and association centers around the 
motor area. This sensory area is not separated from the 
motor area by an association area, as are the other sensory 
centers. We see in this relation of the cerebral centers for 
touch and movement the structural fact which corresponds 
to the functional fact that the skin and other tissues which 
give rise to tactual sensations would naturally, as the earliest 
organs, stand in so intimate a relation to the muscles that 
the later and more highly developed organs of sense could 
not be expected to duplicate this relation. As the primitive 
tactual sensory surfaces came to be supplemented by newer 
and more highly specialized organs of sense, the nervous 
centers for the newer senses were forced to take up more 
remote and complex relations to the motor area, while the 
original senses did not lose the intimate relation which 
they bore from the first. The development of the higher 
senses furnished also opportunity for greater variety in the 


combination of sensory impulses ; consequently the associative 
functions and the areas corresponding to them increased 
with the development of variety in the sensory functions. 
The association centers, which are the structural areas given 
up to the function of working over sensory impulses, natu- 
rally developed between the centers which performed func- 
tions of reception, or the sensory functions, and those which 
performed the functions of motor discharge. The topogra- 
phy of the cerebral centers thus reflects directly the gradual 
evolution of more and more elaborate systems of nervous 

Speech centers. Another group of facts which will serve 
to make clear the character of the association areas is to be 
found by examining that portion of the cerebrum which is 
known as the speech area. This region of the brain was 
first recognized by the anthropologist Broca as intimately 
related to the functions of speech. He found that disease 
in this area resulted in impairment of the patient's ability 
to use or understand language. Later studies of aphasia, as 
the pathological loss of speech is called, have increased our 
knowledge of this area, especially since it has become pos- 
sible through the examination of a large number of cases 
to distinguish a variety of forms of partial aphasia. Thus, 
a person may be able to understand words which he hears, 
but be quite unable to understand words which he sees on 
a printed page. This form of so-called visual aphasia is 
paralleled by forms of auditory aphasia, in which the subject 
is able to read, but cannot understand words which he hears 
spoken. These two forms of partial aphasia indicate that 
the connection between the speech center and either the 
auditory or visual center may be interrupted without destroy- 
ing the connection between the speech center and the other 
sensory area. If the disease of the speech center is strictly 
localized so as to interrupt only its connection with the 
visual center, the other functions may remain intact, while 


the visual forms of recognition of language are interrupted. 
Conversely, if the connections with the auditory centers 
alone are interrupted, visual recognition may continue. 

Turning now to the various forms of motor aphasia, or 
forms affecting the power of expression as distinguished 
from the forms of sensory aphasia mentioned, we find that 
an individual may lose the power of articulation without los- 
ing the ability to write, or he may lose the ability to write 
without losing the ability to articulate. In either one of 
these forms of motor aphasia, the subject may be compara- 
tively free from sensory deficiencies. The lack of ability to 
articulate, when all of the other phases of the function of 
speech are present, shows that the connection with the visual 
and auditory centers may be complete, as well as the con- 
nection with the motor area for the hand movement involved 
in writing, while the motor connection with the center which 
sends impulses to the muscles of the vocal cords may be 
temporarily or permanently interrupted. 

Broca's convolution an association center. Broca's con- 
volution thus turns out to be an association area in which 
a great variety of lines of connection converge. It is not a 
part of the nervous system which acts independently in the 
control of a separate faculty of speech ; it gains its signifi- 
cance in the individual's life as a center for the organization 
of stimulations received in other parts of the cortex and 
transmitted through the cells and fibers of this area on the 
way to the motor area. 

Phrenology not in accord with clearly known facts. It 
may be well to call attention at this point to the fundamental 
distinction between the teachings of phrenology and the dis- 
coveries of modern brain physiology. Phrenology maintained 
that different parts of the brain are given over to different 
faculties. For example, phrenology believed in a certain area 
for the recognition of form, another area for the recognition 
of number, an area for the function of parental love, and one 


for the general trait of combativeness. There is no justifica- 
tion for a theory of localization based upon a subdivision of 
consciousness into such mythological faculties. The cortex 
can be subdivided into areas concerned first with sensory 
impulses, second with motor impulses, and third with organi- 
zation. Conscious processes must be considered as having 
their physiological conditions, not in separate points assigned 
to imaginary faculties, but rather in the organized activity 
of sensory, motor, and association areas. For example, the 
recognition of form naturally includes certain sensory func- 
tions and certain associative processes. The general neural 
basis for such sensory and associative processes we know, 
as has been shown in the foregoing paragraphs. To be sure, 
we do not know at the present time all the details of the 
cerebral map, but the broader outlines are too clearly defined 
to leave any room for mistaken notions with regard to the 
kind of functions which are provided for in the different 
areas of the cerebrum. 

Frontal association area. One area of the cerebrum which 
has been the subject of much speculative discussion is the 
frontal area, or that portion of the cerebrum which lies in 
front of the motor area. In certain cases large portions of 
this area have been destroyed without apparent interference 
with the individual's normal functions. There is a famous 
case known as the American Crowbar Case, in which a 
common laborer, through an accident in blasting, had a very 
large portion of this frontal lobe removed by a crowbar pass- 
ing through the roof of his mouth and out through the top 
of his skull. The individual in question continued to live 
with no serious interruption of his regular nervous or phys- 
ical functions. Such cases as this may possibly indicate 
that the association areas are not fully developed in some 
individuals. In general, it is doubtless true that association 
areas, more than other parts of the nervous system, are left 
open for development through individual experience. If this 


conception is accepted, it is not surprising that an individual 
might be deprived, as in the case cited, of the possibility of 
further development, or even of some of his higher forms 
of association without the loss being obvious to himself or 
to those who observe him. Recent experiments, which have 
been tried in the extirpation of the small frontal area in cats 
and monkeys, show clearly that the frontal area is the part 
of the nervous system involved in newly acquired habits. 
The fact that man, who alone of all the animals has a large 
frontal lobe, is the learning animal par excellence further 
confirms the general view derived from these experiments. 

General principles of nervous action. It remains to call 
attention to a few of the general facts which are known 
with regard to action within the nervous organs. 

Active organs as termini of all nervous impulses. Nerve 
impulses under normal conditions always travel forward in 
the single direction from the sensory centers toward the 
motor centers. There is no reversing of a nervous current. 
If it were otherwise, a central nervous process might travel 
down a sensory fiber and arouse the sense organ. We 
should see colors and hear sounds whenever the central 
system was excited. Under normal conditions this does not 
happen. The sensory impulses come only from the sense 
organs and always move, even though the path be complex, 
in the direction of the motor centers. 

Principle of facilitation. When currents pass through 
the nervous tissue they leave behind paths or tracts which 
facilitate the later transmission of like impulses over like 
paths. Indeed, it seems that in many cases this facilita- 
tion of transmission goes far enough to reduce the length 
of the path. Where the first transmission was over a long 
complex path, later transmissions reach the same end by 
a more direct route. 

Principle of association of centers of high tension. When 
two centers in the cerebrum are in simultaneous action, 


there is a tendency for a path or connection to be set up 
between the two. The active centers may be thought of as 
points of high tension and the currents which they send out 
tend to flow together. 

Diffusion as opposed to organization. Impulses can travel 
through the tissue not merely along the paths which are 
defined by the branches of the cells but also from cell body 
to cell body. This is especially true in the early stages of 
the life of an individual when tracts are not fully devel- 
oped, and it is true at all stages of individual development 
for very strong stimulations. The result of such indefinite 
transmission is a diffuse condition of excitement. Such dif- 
fusion is often the first stage of organization. After a period 
of diffusion, paths are worked out to carry by definite chan- 
nels impulses which at first were spread vaguely through the 
nervous tissue. 

Principle of progressive organization. Under the forego- 
ing principles the nervous system is continually becoming 
more and more highly organized. The effect of experience 
is to be found not merely in the fact that certain paths are 
recorded in the nerve cells, but also in the fact that in their 
totality these parts develop into increasingly complex series 
of interconnections. This is the essential fact which must 
be kept in mind if we would understand the progress of the 
individual from infancy to mature mental life. Each day's 
experience builds up new systems of tracts in the nervous 
tissues and thus leads to higher and higher levels of behavior 
and experience. 

If we keep this formula in mind, we shall be able to 
understand the higher levels of consciousness. Such higher 
levels are always due to the interrelating of lower forms of 
experience. Ideas are made up of related present impres- 
sions and the results of past impressions. Thoughts are 
made up of interrelated ideas. The formula in every case 
is one of more and more complex interrelations. 



Classification derived from study of nervous organs. The 
study of consciousness has often been taken up without the 
preliminary discussion of the nervous system through which 
the foregoing chapters have carried us. It would be entirely 
legitimate, as remarked in an earlier chapter, to begin the 
study of mental processes by looking inward on one's own 
experiences and describing the various facts which intro- 
spection there discovers. The array of facts which would 
thus come to light would, however, be confusing in their 
variety and complexity. It is much simpler to approach the 
facts of mental life with the type of classification suggested 
by the knowledge that sensory processes enter the central 
organs and are there redistributed and organized on the way 
to the motor organs. With this classification to guide us, 
the facts of experience fall into order and lend themselves 
to orderly scientific treatment. 

Classification from observation superficial. An analogy 
will help to make clear the difficulty of classifying facts on 
the basis of unguided observations. If an ordinary man were 
asked to classify the organs of the body, he would begin by 
pointing out the arms and legs as important subdivisions. 
Then he would point out the trunk and head, and so on. 
The student of physiology realizes that these gross external 
subdivisions are, indeed, important but they furnish for 
science an inadequate basis of study as contrasted with such 
fundamental distinctions as those between muscles and bones, 
between organs of respiration and organs of circulation, and 



so on. The moment we divide up the body on these last- 
mentioned lines of functional differentiation we find that 
our science is following productive trains, of description 
and explanation. 

In much the same way popular distinctions of the dif- 
ferent phases of experience must be revised before they can 
be used by science. A striking illustration of this is to be 
seen in the fact that in popular thought pleasure and pain 
are usually treated as facts of the same order, though con- 
trasted in quality. A moment's consideration will make it 
clear that pain ordinarily arises from some definite point in 
the body. It is a type of experience which we classify in 
science along with those experiences which come from the 
stimulations of the skin or the inner surfaces of the body 
and are technically known as sensations. Pleasure, on the 
other hand, has a totally different kind of origin. It is not 
a phase of sensation ; it does not come from particular points 
of stimulation. It must be treated as a type of experience 
which grows out of general organic excitations of a much 
more central character than those which are involved in the 
production of pain. Again, such a term as " attention," which 
has a large practical use in ordinary life, is one of the most 
confusing terms when it is carried over into scientific study. 
If one recognizes, as he must in psychology, that attention 
is capable of a great variety of different degrees, he will find 
it possible to extend this term over every possible experience. 
There are forms of intense and vivid consciousness for which 
some term, such as "vividness " or "attention," is undoubtedly 
required in science. There are other forms of consciousness 
which are relatively vague and indistinct, yet when dealing 
with these cases we cannot fail to recognize the necessity of 
using the word " attention " or some such phrase as " low 
degree of attention," if we have adopted the word into our 
scientific vocabulary. These illustrations make clear the 
problem which confronts psychology when the attempt is 


made to secure an analysis which is at once satisfactory 
for purposes of scientific treatment and explanation and in 
keeping with ordinary introspective observations. 

Historical threefold classification. In the history of psy- 
chology many efforts have been made to develop an appro- 
priate scientific classification of mental processes. One of 
the classifications which was for a long time generally ac- 
cepted is that which grouped all forms of experience under 
the three general heads of knowledge, feeling, and volition. 
There can be no doubt that such a threefold classification 
describes certain fundamental differences in conscious ex- 
perience. The man who is engaged in thinking out some 
problem of science is certainly not at that moment absorbed 
in an intense feeling or emotion. On the other hand, the 
man who is thoroughly angry over some situation which has 
arisen is by no means in a condition to consider logically 
and judiciously the facts which appeal to his thoughtful 
neighbor who is free from emotional excitement. It is some- 
what more difficult to justify the classification of volition as 
different from knowledge and feeling, for no serious thought 
is possible without some voluntary effort, and no emotion 
ever arises without inducing some form of action. Yet, 
even though volition is intimately interwoven in all forms 
of knowledge and feeling, there are certain cases of decision 
which are not to be regarded as typical processes of know- 
ing, or processes of feeling; hence the term "volition" is 
needed for a full description of mental activities. 

Historical twofold classification. Another somewhat dif- 
ferent type of classification has been used by certain writers ; 
according to this, only two different types of experience 
are distinguished ; namely, knowledge on the one hand, and 
active processes on the other. This twofold classification 
offers less difficulty to explanatory science than the three- 
fold classification, because it is more general. In bringing 
together a great variety of facts under the active processes 


so called, we are freed from the necessity of making any 
sharp distinction between the feelings, which are undoubtedly 
active aspects of consciousness, and decisions, which from 
any point of view must be regarded as active. 

Without ignoring in our later discussions the historic dis- 
tinctions between knowledge, feeling, and volition, it will be 
possible to draw from our study of the nervous system a 
more productive classification. 

Classification according to nervous processes. The most 
fundamental fact discovered with regard to nervous struc- 
tures was that they couple the sense organs with the organs 
Df behavior. Consciousness arises during the translation of 
i sensory impression into a motor response. Every conscious 
process will, first of all, have certain aspects which are due 
to the sensory impression and, second, certain other aspects 
which are related to the motor response. 

Third, every nervous process in its passage from the sense 
organ to the point of discharge encounters certain other 
nervous processes and is fused with them. Consciousness 
is in an important sense the result of fusions of many 
impressions. Whoever would understand the facts of experi- 
ence must ask how they are built up out of the combination 
of many elements. We must study, therefore, the fusions 
which condition conscious phenomena. 

Fourth, every sense impression on its way to the motor 
discharge is modified in character by past processes in the 
nervous system. The past is brought over into the present 
by the structural changes which are recorded in the nervous 
system and influence every new impression in its passage 
through this system. 

Fifth, the most impressive lesson which was drawn from 
the study of the evolution of animal forms was that in the 
highest nervous systems great areas are set aside for a type 
of indirect recombinations which are of such importance 
that they must be distinguished from the fusions referred to 


under third^ above. The recombinations due to the action 
of the association areas are of a higher order and are to be 
distinguished as indirect or abstract processes. 

Example of scientific analysis and classification. The 
classification of facts here outlined will, perhaps, be better 
understood if an example is used. Let one look at a printed 
word. The experience which results may seem to the un- 
thinking observer to be a single simple process of recog- 
nition. A moment's consideration will bring out endless 
complexities. In the first place, the experience breaks up 
into impression and interpretation. There is a part of the 
word-consciousness which comes from the page, a part which 
comes from past experience. The part of the experience 
which comes from the page proves on closer examination 
to be complex. There are black and white impressions in 
sharp contrast with each other which fuse into the complex 
image of letters and unite into a single image of a word. 
There are motor tendencies which often are vivid, one 
tends to say the word, or there is an incipient impulse to 
obey its dictates as one realizes in one's own experience 
when the word "down" is contrasted with the word "up." 
Finally, the meaning calls up elaborate thought-processes 
which carry one far beyond the present word and arouse 
associations of indefinite complexity. 

This example serves to show how even superficial study 
of a single experience demonstrates the necessity of some 
plan of classification under which the various aspects of a 
mental process may be described and explained. Further- 
more, the example is a fortunate one with which to demon- 
strate the importance of those indirect elements of experience 
not derived from sensation. The impression is the least 
important part of the word-consciousness. Our scheme of 
classification is important not merely as a means of securing 
a complete description but also as clue to the scientific ex- 
planation of mental processes. The student of psychology 


must constantly keep in mind the necessity of standing 
outside himself and getting a true perspective of his mental 
processes. One is likely to overemphasize the impression 
which comes from without and to overlook one's own con- 
tribution ; it is accordingly the business of scientific psy- 
chology to restore the balance and give a true emphasis to 
that which comes out of past experience and that which is 
due to the central and motor processes which attach to the 

Relation of classification to introspection. The classifica- 
tion of psychological problems is therefore frankly borrowed 
from the clue furnished by the study of the nervous system 
rather than left to the accidents of introspection. Intro- 
spection will not be ignored, but the facts derived by looking 
into experience will be ordered according to the formula 
derived from objective studies. Perhaps a more fortunate 
method of expression will be to say that the classification 
having been determined through a study of nervous struc- 
tures, introspection will be used to reveal the classes of facts 
which the study of the nervous system teaches are important. 

Sensations. First we shall seek facts of sensation. Im- 
pressions come to us from the outer world through each 
of the senses. Red, green, a shrill sound, a musical tone, 
an odor, a taste, a pressure against the skin are typical 
cases of this class. There is no difficulty in justifying an 
examination of sensations. 

Reactions and attitudes. Then there are reactions to 
sensations. In some cases these reactions are very direct ; 
this is true where the whole process is simple. Most ex- 
periences have grown very complex and the reaction to the 
impression comes only after an interval during which the 
sensation has been coupled with many other factors of 
experience. It is sometimes extraordinarily difficult to de- 
termine how reactions are related to impressions. The 
psychologist finds it better in such cases to postpone the 


full discussion of reaction until after he studies the complex 
of facts added to sensory impressions. A complete post- 
ponement of the study of reactions would, however, make 
difficult the explanation of those simple processes in which 
the reaction follows directly on the impression. The reac- 
tions will therefore be taken up first in an introductory 
way in chapters immediately following the treatment of 
sensations, and later the topic will be amplified by a study of 
the mote remote and complex forms of organized reaction. 

The conscious fact which parallels a reaction deserves 
a name. The word " attitude " serves very well this pur- 
pose. We say in common parlance that we feel an attitude 
of interest or disgust. Our study will show us that all atti- 
tudes of mind are aspects of consciousness related to reac- 
tions. We have attitudes of belief and incredulity, attitudes 
of sympathy and aloofness. All these are as distinct from 
sensations as facts of consciousness can be from each 
other. We shall attempt a classification of some of the 
more fundamental attitudes. 

Fusion and perception. The term " fusion " suggests cer- 
tain simple combinations of sensory facts such as the recog- 
nition of an orange as the source of a certain color, a 
certain odor, a taste, and a sensation of roughness to the 
touch. In experience all these qualities fuse. They are 
located together in front of us or at the side. They make 
up our experience of an object. We speak of the expe- 
rience as a sense percept. 

Memory. The term "memory" includes a great many 
factors of which we make use, but which we seldom unravel 
from the complex of present experience. One meets a 
friend, and past experience, unnoticed as a separate aspect 
of mental life, determines one's whole recognition. One 
reads into the present all the pleasant associations of earlier 
days. On other occasions one labors to call up some for- 
gotten or half-forgotten fact. The effort to recall makes 


one actually aware of the distinction between the present and 
the past. Here is an opportunity in treating of memory to 
draw productive distinctions between many different kinds 
of memory. 

The process of ideation. There are ideas and combina- 
tions of ideas which constitute the highest forms of men- 
tal activity. The idea which one has when he thinks of 
honesty is something more than sensation or attitude or 
memory ; it is the understanding of a whole series of rela- 
tions. We speak of this as an abstract idea, meaning by 
that term that we have cut loose from impressions and are 
in a world of our own making. The processes of abstrac- 
tion exhibit the creative power of a highly developed indi- 
vidual as no other mental process can. The animals do not 
have, so far as we can judge, abstract ideas. They have 
sensations, attitudes, percepts, and memories, but their 
powers of organization stop short of abstract ideas. 

How one forms an abstraction is extremely difficult to 
observe through mere introspection. A mind absorbed in 
studying geometry cannot observe itself at work. That 
is why abstract geometrical ideas are difficult to explain. 
Obviously, however, the system of psychology which omitted 
these would be altogether deficient. 

Higher forms of action. After dealing with the processes 
of ideation we may very properly come back to a reexam- 
ination of behavior. Those forms of behavior which are 
characteristic of mature intelligence are commonly grouped 
together under the caption "voluntary choice." The discus- 
sion of voluntary choice will not duplicate the treatment of 
reactions and attitudes as indicated on page 66. 

Relation to historic classification. The foregoing classi- 
fication is to be followed in the following chapters. For the 
sake of keeping it in some relation with the historic classi- 
fications, it may be said that the term " knowledge " is in 
a measure synonymous with sensation, perception, memory, 


and ideation. Feeling and volition are, roughly speaking, 
synonymous with attitudes, while the higher forms of be- 
havior classified under voluntary choice are quite synony- 
mous with the higher phases of volition. The effort should 
not be made, however, to push this reconciliation of the 
two classifications too far. There is a large element of 
effort and hence of volition in every fusion and every 
formation of an abstraction. There is a large element of 
feeling In most perceptions. The adoption of a classifi- 
cation of psychological facts based on studies of nervous 
processes is a frank abandonment of the historic threefold 

Practical applications. Following the study of the various 
classes of psychological facts will be certain studies of a 
practical type which may be termed applications of psy- 
chology. A part of these applications will be formulated 
with a view to helping the student to see his own mental 
processes from a psychological point of view. A part will 
deal with some of the larger social problems, with a view to 
showing that community life is capable of proper organiza- 
tion only through a complete understanding of the nature of 
human consciousness. 


The following summary of the foregoing discussion will serve 
as a guide to the subsequent chapters : 

I. Sensations 

This will require a description of -the sense organs and their 
action and a description of those aspects of consciousness which 
come as impressions from the outer world. 
II. Attitudes 

This will require an explanation of the relation of consciousness 
to bodily activity and a classification of forms of conscious ex- 
periences which arise as a result of the individual's reactions to 


III. Fusions of Sensations 

As sensations become motives or sources of reactions they are 
united into complexes. These complexes are called percepts and 
are always present where an individual distinguishes objects in 
the world about him. 

IV. Memories 

Past experiences are retained in structural changes in the 
nervous system and either in explicitly distinguishable form or in 
less obvious character enter into present experience. Psychology 
must include under this head many facts which escape introspec- 
tion. Here as elsewhere throughout the discussion the largest 
regard must be had for the fact that the explanatory prin- 
ciples of psychology depend on a clear understanding of motor 

V. Ideas and Ideational Forms of Thought 

These include all the higher forms of organized experience. 
They are conditioned by the higher complexes which are de- 
veloped in the cerebral association areas. 

VI. Voluntary choice is the phrase employed to mark off the highest 
forms of behavior from the lower forms. The concept of 
personality enters into this discussion. 
VII. Applications to individual experience and to social organizations. 



Sensations not copies of external forces. For the ordinary 
man there is no problem for psychology presented by a 
sensation. A sensation is for his thinking an inner reflec- 
tion or copy of an external fact. He dismisses as curious 
speculation any statement which would tend to impair his 
confidence in the directness of the relation between sensar 
tions and external or objective facts. Yet, as was pointed 
out in an earlier chapter, the progress of science has forced 
upon us a distinction between objective colors and sounds, 
on the one hand, and subjective or experienced sensations 
of color and sound, on the other hand. For example, color 
as we see it in our individual experiences is not a form of 
vibration, while color as the physicist finds., that he must 
describe it in order to explain its physical nature is a form 
of wave motion easily convertible into other wave motions, 
such as those of heat, which in turn give us sensations of 
a sort quite different from colors. 

Laws of sensation as one of the first problems in psychol- 
ogy. The moment we admit a distinction between subjec- 
tive color and external light vibrations, certain important 
scientific questions immediately suggest themselves. Thus, 
we are led to inquire what are the laws of subjective color 
as distinguished from the physical laws of objective light? 
For example, in passing from one color in the subjective 
series to the next color, as from red through orange and 
yellow to green, we find ourselves taking a series of steps 
and reaching qualitative differences so marked that we 



speak of the sensations as opposite or as sharply contrasted. 
This marked difference in qualities is related to animal 
interests of a practical sort. Red fruits and green are to be 
distinguished ; the color of the foliage and of the blossom 
are to be discriminated. In physics, the transition from the 
red vibration to the green is one continuous series of changes 
in rate of vibration. All the vibrations are qualitatively alike; 
there is no contrast. So far as light vibrations are concerned, 
they are utterly heedless of animal interests. 

Another example of the difference between the subjec- 
tive series and the physical scries is to be found in the fact 
that sensations arise only from the middle of certain physi- 
cal series. Thus the physicist knows that there are rays of 
light made up of vibrations slower than those which give 
us sensations of red, and that other rays are more rapid in 
vibration than those which give sensations of violet. The 
range of sensations of sound, in like fashion, is short, con- 
trasted with the series of sound vibrations known to the 

Relation of sensations to sensory nervous processes. The 
relation between sensations in consciousness and physio- 
logical processes in the organs of sense is much closer 
than is the relation between sensations and the physical 
facts above discussed. Thus, to take a striking illustration, 
it is because we have an organ of sense which is affected 
by light and no special organ affected by weak currents of 
electricity that men overlooked for so long a period both 
the prevalence of forms of electrical energy and the close 
relation between light and electricity. Such an illustration 
calls attention to the fact that experience differs in certain 
of its aspects from the physical world, because experience 
is related to the physical world only indirectly, through the 
organs of sense. 

Other examples are abundant. When the ear is aroused 
by the complex sound coming from a drum and a trumpet, 


there are sensations corresponding to each element of the 
complex because the sensory cells receive the vibrations 
from one instrument at one point and the vibrations from 
the other at another point. The two elements of sound 
do not obliterate each other or cause a blur in conscious- 
ness. They do not give rise to a single sensation, even 
though the sound wave which strikes the ear is a single 
complex air vibration. The further details of this matter 
will come out in later sections of this chapter. 

Sensations as elements. Our first problem, then, is to 
study sensations as related to the facts of physics and to 
the facts of physiology of the sense organs. I^ater, we 
shall study sensations in their relation to one another and 
to the higher forms of experience. It will then be pointed 
out that sensations as they appear in consciousness are 
always elements of complex forms of knowledge. There i 
no such experience as an isolated sensation of red or of 
green or of sound. All sensations are referred to some 
point in space ; they are associated with certain interpreta- 
tions and otherwise brought into the stream of personal 
experiences. But in all these later combinations, sensations 
retain their qualitative independence to an extent which 
justifies us in recognizing them for the purposes of science 
as elements, or separate and distinct aspects of conscious- 
ness. The problems of fusion of sensations with each other 
and the laws of these fusions may therefore properly be 
postponed ; for the present, we turn to a discussion of sen- 
sations as elements of consciousness related to certain facts 
of physics and to the processes in the organs of sense which 
lie between the physical world and consciousness. 

Psycho-physics as a division of psychology. The field of 
study which we here enter has sometimes been called 
psycho-physics. This name originated as the name of one 
branch of the study of sensations to which our introductory 
examples have not referred. Psycho-physics in its earlier 


days studied especially the facts of intensity of sensation. 
If a physical sound becomes stronger, it does not follow 
that the related sensations will become stronger in a corre- 
sponding degree. The facts of intensity will be referred to 
briefly in our later discussions. 

In taking up the problems of psycho-physics, we shall 
begin with one of the most highly developed and highly 
differentiated groups of sensory processes ; namely, those of 
vision. We might have taken first the simpler sensations, 
such as those of touch, but the facts regarding color are so 
much more complex and significant that it will be advanta- 
geous to encounter at once all the major principles involved 
in such a study. 


Meaning of term f< quality." Visual sensations, like all 
sensations, can be described only to a perspn who has 
experienced them. Red and blue and yellow and black are 
names of visual sensations. If the reader has had experi- 
ences corresponding to these words, he will recognize that 
each of the experiences referred to is a unique fact in his 
mental life. Red may be like orange or yellow ; it may be 
soft and pleasing, or glaring and unpleasant ; but its essence 
Is its redness, and this essence, which is called the quality 
of the sensation, can be illustrated but cannot be defined in 
terms of any other experience. 

Chromatic (or color) series and achromatic (or gray) series. 
If we consider all possible visual sensations, we notice at 
once that there are two general groups, those which 
belong in the series of colors and those which belong in the 
black-gray-white series. The latter series is in some respects 
the simpler. Beginning with the darkest black, one may 
arrange various shades of gray in an unbroken series up to 
the brightest white. The color series is more complex. It 
i* made up of sensation qualities which, to be sure, shade 


into each other through intermediate colors ; but the members 
of the series have a marked individuality which leads us to 
designate them by a variety of entirely different names 
rather than by a common term, such as is used in referring 
to the gray series. Thus, red and yellow are different quali- 
ties, though they shade into each other through orange; 
when we pass from one to the other, the transition is so 
marked that we are compelled to describe red and yellow as 
different, qualities. 

Fundamental color names. The question of how many 
fundamental visual qualities there are, is one that has often 
been discussed. Popular language has clearly marked out 
at least four color qualities besides the blacks, grays, and 
whites. These four colors are red, yellow, green, and blue. 
The names of these colors are, as their form clearly indi- 
cates, older than such derived names as orange, indigo, 
violet, or any of the compound names, such as green-blue 
and yellow-green. The loose use of the four older color 
names makes it clear, however, that there is no particular 
red or green which can be selected as having exclusive right 
to the name. In making up a system of color terminology 
for such works of reference as a dictionary, this fact comes 
out very clearly. The best that can be done is to take the 
average of a large number of usages and exhibit a sample 
of the color chosen. Color names, therefore, while suggest- 
ing something of the popular discrimination of colors, supply 
no final evidence as to the number of primary sensation 

The various scientific studies on this subject of the number 
of color qualities may be divided into three groups. One 
group regards red, green, and blue as the only primary 
colors, all others being looked upon as derived forms. A 
second group adds yellow, while a third group considers that 
there are an indefinitely large number, certainly more than 
four. The solution of the question, since it does not depend 


merely upon introspective observation, waits upon the com- 
plete formulation of certain facts discussed later. 

The color spectrum and circle. More important than the 
determination of the exact number of primary color qualities 
Is the presentation of a complete description of the series 
of color experiences. The most complete single series of 
colors known to physics is produced by passing a pencil 
of white light through a prism. The different colors which 

compose this ray of 
white light will be 
refracted to different 
positions, and the 
whole will be spread 
out into a colored 
band with red at one 
end and violet at 









FIG. 23. Color circle 

The center of the circle represents white. All colors 

placed at opposite ends of diameters of the circle 

are complementary colors 

fGreemsh the Other. 

Blue . .. , 

these lie orange, yel- 
low, green, blue, in 
the order given. 
This whole series of 
colors produced from 
white light is called 
the spectrum. Mixed 
colors are not present in the spectrum, notably purple, which 
consists of a mixture of red and blue. When purple is intro- 
duced, the series of colors seems to return upon itself. For 
this reason, the colors of the spectrum plus purple may con- 
veniently be represented by a closed figure, either a triangle 
or a circle. The color circle is given in Fig. 23. Four, or 
better nine, color names are used to indicate some of the 
chief qualities of the series, the exact number of such quali- 
ties being left somewhat indefinite, for reasons indicated 
above. Between the colors explicitly named in this circle 
there are transitional forms of sensations. 



Saturation, brightness, and mixtures. There are also 
transitional forms of sensation from this color series to the 
gray series. Thus, from any color there is a series of sen- 
sations in which the color quality gradually fades into a 
colorless gray of the same intensity as the original color. 
Such a series is called a saturation series. The full color 
is said to be a saturated quality ; the more the quality ap- 
proaches gray, the less saturation it is said to have. Each 
color is also capable of variations in brightness. A red of 

FIG. 24. Wave forms 

great light intensity is said to have a high degree of bright- 
ness. A color of small light intensity is said to have a low 
degree of brightness. The relation of brightness to satura- 
tion is such that when a color becomes very bright or very 
dim its characteristic quality tends to disappear. Finally, 
color qualities may be compounded so as to produce a great 
variety of intermediate qualities, such as orange-yellow and 
blue-green, which are sometimes thought of as intermediate 
qualities, sometimes as equally primary with the others. 


External light. Turning now from the series of visual 
sensations, let us review very briefly the characteristics of 
external physical light. The physicist recognizes physical 
light #s a form of vibration in the luminiferous ether. These 
ether vibrations have three characteristics ; namely, rate of 
vibration, amplitude of vibration, and complexity of vibration. 
For purposes of exposition we may compare light waves to 
simple water waves, which are represented in outline in 
Fig. 24. In waves of this type a single particle of water 
oscillates up and down in straight lines, while the wave as 
a whole travels in the horizontal direction. 

The rapidity with which each particle oscillates is called 
the rate of vibration. The rate determines the length of 
the waves from crest to crest, so that we may refer to waves 
as having different lengths : rapid vibrations corresponding 
to short wave lengths, and the slow vibrations corresponding 
to greater wave lengths. The amplitude of a wave is de- 
termined by the extent of the oscillations of each particle. 
The complexity of a wave depends on the mode of the 
movement of the particles ; a complex movement results 
from the action of a number of wave impulses acting on the 
same particle at the same time. 

The wave forms represented in A, Fig. 24, have like 
amplitude that is, like range of movement above and below 
the horizontal line but differences in rate, one wave being 
twice as rapid as the other. The waves in B are alike in 
rate but different in amplitude. The lines i, 2, 3, 4, 5, 6 
show the paths of six single particles which participate in 
the larger wave motion. When a particle is in its original 
position, it lies at some point along the horizontal line, as 
at O. At successive periods it moves to the height I, 2, 
or 3 or to the low level 4, 5, or 6. C represents a complex 
wave form. The two regular waves, indicated in dotted lines, 
acting upon the particles together, result in the complex 
form of vibration represented in the full-drawn line. 



Comparison of physical and mental series. In the follow- 
ing table a comparison is exhibited between the physical facts 
and the corresponding facts of sensory experience : 

Pnvsu'Ai KALIS 


Simple light vibrations of medium 

These simple vibrations appear in 
every possible rate, thus forming 
a single continuous scries of varia- 
tions in rate 

These rates vary from less than 
435 million million vibrations per 

(435 million million vibrations per 

through all possible rates 

to 769 million million vibrations 

per second 
and beyond 

Compound vibrations 

The compound sometimes consists 
of vibrations of about 435 to 500 
million million per second, com- 
bined with those of about 660-769 
million million per second 

In some cases widely different rates 
are combined, sometimes in special 
pairs, sometimes in more complex 

In some cases various rates other 
than those above mentioned are 

Amplitude variations 

Increase in amplitude to the highest 

Decrease in amplitude to the lowest 

Color sensations 

The sensations differ in certain well- 
marked stages, forming a series 
of distinct color qualities, limited 
in number 

No color experience (sometimes 
experience of warmth) 


Successive qualities (yellow, green, 


No color experience 

Either whites, grays, less saturated 

colors, or purples 

White or gray 

Various grays and unsaturated colors 

Changes in intensity and saturation 
Increase in intensity and decrease 

in saturation toward white 
Decrease in intensity and in satura- 
tion toward black 


Relation between the physical and the psychical facts 
dependent in part on the organs of sense. The differences 
between the physical series and the sensation series are so 
striking that much scientific investigation has been devoted 
to the effort to bridge over the differences, as far as possi- 
ble, by setting between the two groups of processes described 
in the above table a third group of processes ; namely, the 
physiological processes in the eye and central nervous sys- 
tem. Not infrequently it has been impossible, with the 
means of scientific investigation in our possession, to dis- 
cover by direct observation all the physiological links be- 
tween certain physical facts and certain facts of experience. 
In such cases, theories have been developed by science to 
fill the gap. These theories go beyond direct observation 
in their statements, but do so with definite regard to such 
facts as can be observed. We turn, therefore, to a con- 
sideration of some of the physiological facts- and theories, 
taking up, as a necessary introduction to the physiological 
faj;ts, a study of the structure of the eye. 

Evolution of organ of vision. The human eye is a very 
complex and highly sensitive organ. It will be well for us 
in attempting to understand the eye, to go back to an earlier 
point in the evolutionary series and begin our study with 
more primitive visual organs. (The line of evolution between 
the simplest eyes and the human eye is not direct, for the 
human eye is in its sensitive parts a division of the brain 
brought to the surface of the body. The eyes of inverte- 
brates show, however, how sensitivity to light first became 
a specialized function of animal tissue./ 

^Even in the lowest forms of plant and animal life there 
is a certain sensitiveness to light. A flower is affected by 
light, in some cases enough to produce movement on its 
stem, in all cases in its inner growth conditions. So also the 
unicellular animal forms are stimulated by light to vigorous 
action. In the simpler multicellular animals, in addition to 


the differentiation between neural cells and muscular cells 
which was described in an earlier chapter, there is a further 
differentiation among the neural cells. In the jellyfish, for 
example, it is found that at certain points on the surface of 
the body the cells of the nervous system are grouped into 
small spots of pigmented cells (see Fig. 25, A). The pig- 
ment is not a part of the nervous system, but it serves to 
absorb the light which falls upon this part of 4he animal's 
body more than do the unpigmented regions.y The result 
is that the influence of the light is enhanced by the pres- 
ence of the pigment, and the growth of larger and more 
sensitive sensory cells in the immediate neighborhood of 
these spots brings about a condition which is favorable to the 
reception of light. We may, for convenience, refer to the 
pigment, since it is not true nervous tissue, as an accessory 
organ. We shall find in the study of later developments of 
the eye that the accessory parts of the eye are quite as im- 
portant as the nervous organs themselves, the evolution of 
the two groups of structures going on in parallel lines. 

Higher forms of visual organs are represented in Fig. 25, 
B and C. Thus we find a larger group of cells sensitive to 
light stimulations. (The pigment is present as in the most 
primitive eyes, and me whole organ is placed in a depression 
in the surface of the body.) This depression serves to protect 
the delicate cells more effectively than they could be pro- 
tected on the general body surface, as in the case of the 
jellyfish. This protection of the cells undoubtedly works to 
the advantage of the cells, furnishing them the conditions 
necessary for becoming more sensitive, while at the same 
time the wall of the depression furnishes them the space in 
which they become more numerous. In later stages of de- 
velopment, as indicated in Fig. 25, D and E, the depression 
in the body wall is filled with a protecting fluid. This fluid 
is of a thick, gelatinous consistency, and in the most primitive 
forms translucent, not transparent. The light stimulation 

FIG. 25. A series of eyes which have reached various levels of development* 



which acts upon the sensory cells of such an eye as this 
will obviously not be very intense or definite. Something 
has been sacrificed to protection in the fluid, which obstructs 
the light. This disadvantage is, however, more than offset 
by the fact that the fluid furnishes favorable conditions for 
increase in the number and sensitiveness of the cells. Such 
an eye as this cannot distinguish more than vague changes 
in illumination. An opaque object passing before the animal 
might, by its shadow, be recognized as something standing 
between the animal and the light, but the form or distance of 
the object certainly could not be recognized except through 
the intensity of the shadow and the period of its duration. 
A bright object would give a somewhat more definite im- 
pression, but nothing comparable to the impression received 
by the eyes of the higher animals. 

Later stages of development of the eye are represented 
in the figure. In Fig. 25, D, E, and /% it will be seen that 
the outer covering of the eyes begins to develop a lens. In the 
earliest forms, this lens is spherical in shape. Such a shape 
is mechanically simple, but optically very imperfect. The 
image which it throws on the sensory surface is distorted, 
and the different rays of light are focused at different points, 
causing the hazy colored fringes technically known as chro- 
matic aberrations. 

Organ of sense as selective organ. Such an evolutionary 
series as that just described could be made the basis of a 
chapter on the relations of the animal's inner life and 

* Fig. 25, A, shows a simple pigment spot. The ordinary epithelial cells which con- 
stitute the surface of the body are represented at a. The pigment particles repre- 
sented at pa make this portion of the surface of the body more susceptible to the 
action of light. Fig. 25, B, shows a somewhat more highly developed organ. The 
surface of the body is here depressed so as to protect the sensory cells. These 
specialized cells are notably larger than the epithelial cells at aa. This is the eye 
of Patelia. Fig. 25, C, represents the eye of Nautilus. The central cavity is filled 
with water. Fig. 25, Z>, is a camera eye with a large lens filling its cavity ; <?/ repre- 
sents the lens. Fig. 25, E, is the camera eye of Murex with the cornea, c, covering 
the lens. Fig. 25, F, is the complete eye of cuttlefish with the lens, /; cornea, c\ 
iris, i, and other portions as before. (From Conn's Method of Evolution") 


development to the outer world of nature. Evidently it is 
greatly to the animal's advantage to be sensitive to changes 
in light and thus also to gain indirectly impressions from all 
objects which reflect or absorb light. The inner life processes 
are very dependent on these impressions ; therefore, a part 
of the organism is set aside to keep watch and guide the 
organism. The organism is thus enabled to select from 
the world in which it lives those impressions which have to 
do with its own existence. Furthermore, as we shall find 
when we come to study other organs of sense, other parts 
of the body surface are specialized ta keep the animal in 
contact with aspects of the outer worn other than light. 
The organs of sense are accordingly to be defined as special- 
ized avenues through which forces of the external world 
that are important to the animal's life affect the organism. 

The human eye its muscles. We pass over the varying 
forms of visual organs exhibited in the animal world and 
take up briefly the human eye. The human eye is an inde- 
pendent organ separated from the body wall and placed in 
a protecting bony cavity or eye socket. Before taking up 
the internal structure of the eyeball it may be well to refer 
to the external muscles which hold it in place and move it 
about independently of the head. These are important acces- 
sory organs and increase the range of vision greatly by mak- 
ing it possible to move the eyes easily without moving the 
head. The human eye is supplied with six such muscles. 
By means of these muscles the eye is capable of rotation, 
with the nicest adjustments in any direction whatsoever. 
In ordinary life the behavior of one eye is closely related 
to the behavior of the other eye, so that the muscles coop- 
erate in producing certain joint movements, or binocular 
movements as they are called. 

Many of the facts of human vision are closely related to 
the fact that the eyes are themselves very active organs. 
Looking at an object involves a great deal of muscular 


adjustment. Looking to the left involves a different type of 
muscular adjustment from that involved in looking straight 
ahead. These facts should be borne in mind as important 
for much of our later study. 

The outer wall and the lens. A sectional view showing 
the internal structure of the eyeball is given in Fig. 26. 
It will be noted immediately that this organ is in many 

FIG. 26. Diagrammatic section of the human eye 

0, optic nerve ; 5, sclerotic ; C, cornea ; A, choroid coat ; /, iris ; R, retina ; V, vitreous 

humor ; H, aqueous humor ; L, crystalline lens ; X, optic center of the lens ; , blind 

spot ; /, fovea centralis ; /, pupil ; A/, ciliary muscles, which control the curvature 

of the lens ; Qb^ object outside of eye ; /m, image on the retina. (After Wundt) 

respects more highly developed than any of the eyes repre- 
sented in Fig. 25. By the development of an independent 
outer wall of cartilage the eyeball has been made a free 
portion of the body, as noted in the last paragraph. In the 
second place,, it will be observed that the lens, which we 
saw in some of the lower forms as a spherical organ, has 
been elaborated in the course of animal evolution, so that it 
now has the very much more advantageous form of a double 
convex lens, indicated in the figure at L. This lens has 
certain other complexities in structure which tend to free it 


from optical defects. It is not homogeneous throughout ; 
furthermore, by means of the iris, or adjustable diaphragm, 
which is placed in front of it, only the center, which is the 
most efficient portion of the lens, is utilized in ordinary 
vision. By means of certain muscles which form a circle 
around the lens and control a transparent capsule which 
surrounds it, the lens can be modified in form so that it is 
made more or less convex according as light which is to be 
focused upon the sensory surface comes from a source near 
at hand or far away. The details of this adjustment of the 
lens need not be discussd here ; it is enough to call atten- . 
tion to the fact that when the eye is to look at an object far 
away, the lens is relatively less convex than when the eye 
is looking at an object near at hand. The adjustment is 
carried out reflexly. There are limits beyond which it is 
impossible for the lens to adjust itself ; the near limit for 
the normal eye is about eight inches from the eye, the re- 
mote limit for the normal eye is at an infinite distance. 
Individual imperfections in adjustment appear. For example, 
the lens in old age becomes somewhat less elastic than in 
early life and, because of this lack of elasticity, it is incapable 
of taking on a high degree of convexity. Other abnormali- 
ties appear, in that the far limit of certain eyes is at a rela- 
tively short distance in front of the eye ; a person whose 
limit of remote vision is thus nearer than a point infinitely 
far away is described as near-sighted. Most of the defects 
in the functioning of the lens can be relieved more or less 
completely by the use of an artificial lens outside of the eye. 
The function of the artificial lens is exactly that of the lens 
in the eye, and the possibility of correcting defects in the 
lens of the eye by various combinations of glass lenses is 
limited only by the possibilities of physical optics. This 
makes it perfectly clear that the lens is not to be treated 
as a part of the nervous system but rather as an accessory 
organ developed for the purpose of applying the stimulus 


to the organ of sense in such a way as to produce a clearly 
defined image on the retina. 

Transparent media. In the human eye all of the media 
through which the light must pass are highly transparent. 
A certain portion of the outside coat of the eye namely, 
that portion which lies directly in front of the lens is trans- 
parent. Between this transparent wall, or so-called cornea, 
and the lens of the eye there is a chamber filled with trans- 
parent fluid known as the aqueous humor. The lens itself 
is of a very high degree of transparency. Back of the lens 
is a mass of gelatinous matter known as the vitreous humor, 
which fills the whole eyeball and maintains the proper 
spherical form of the eyeball. These transparent media are 
products of evolution and show an important advance over 
the translucent gelatinous substances which we find in the 
more primitive eye. 

Choroid coat. The pigment layer which was seen in the 
most primitive eyes is present in the human eye in the so- 
called choroid coat. It covers the whole inner surface of 
the eyeball. It serves the same purpose as does the black 
lining of a camera; that is, it prevents the rays of light 
which have acted upon the sensory surface from being 
reflected back so as to interfere with other entering rays. 
It is richly supplied with blood vessels, which provide for 
the nutrition of the sensory cells. 

The retina. We have, up to this point, referred only to 
the accessory organs of the eye. We turn now to the exam- 
ination of the retinal surface, which is the true sensory 
organ. It is made up of a series of layers of cells dis- 
tributed over the inner surface of the eyeball and placed 
between the choroid coat and the vitreous humor. The 
retinal layer is represented in section in Fig. 27. The rods 
and cones, which constitute the inner layer lying next to 
the choroid coat, are undoubtedly the organs which are 
most immediately affected by the rays of light. The rods 



and cones are highly developed cells which are specialized 

for the reception of light stimulations. They may be 

thought of as small ves- 
sels containing chemical 
substances which are 
especially susceptible to 
changes under the action 
of light. The chemical 
activity set up in the rods 
and cones by the light 
which enters the eye 
liberates energy, which 
is transmitted through 
the successive layers of 
cells represented in the 
figure until, finally, it 
reaches the large nerve 
cells of the retina, indi- 
cated at the level VIII in 
the figure. The energy 
which originally entered 
the eye in the form of 
vibration in the luminif- 
erous ether is thus trans- 
formed into chemical 
action in nerve cells, and 
the chemical action in the 
nerve cells is transmitted 
to the fibers which pass 
out of the eyeball and 
communicate with the 
central nervous system. 
Rods and cones and their functions. The rods and cones 

undoubtedly represent different types of receiving organs. 

The central part of the retina, which is more important for 

FIG. 27. 

A diagrammatic section of the 

/ is the pigment epithelium, // is the layer of 
rods and cones. The rods are the small, slender 
organs. In the retina the rods and cones are, 
throughout the larger part of the organ, mixed 
together; in the fovea only cones appear. ///, 
7K, V, F7, VII show various intermediate struc- 
tures between the rods and cones and the nerve 
cells which are situated at 17 fL From the nerve 
cells at VIII the optic fibers pass out, as indi- 
cated at IX, toward the blind spot, where they 
leave the eyeball. A' represents the limiting 
membrane of the retina. A ray of light entering 
the eye passes through the retina in the direc- 
tion from X to 77. The light does not produce 
any effect upon the cells or fibers until it reaches 
the layer of rods and cones. (After Greeff) 


clear vision than other portions, is made up of cones exclu- 
sively. Passing from this limited central region of clear 
vision, known as the fovca c entrails, toward the outer areas, 
or periphery, of the retina, the rods become more and more 
numerous. The functional differences which correspond to 
these structural facts can be easily observed. Let a colored 
light of moderate size and intensity be brought into the 
outer part of an observer's field of vision. This light will 
cast its itnage on the periphery of the retina where the rods 
predominate, and the observer will not experience a color 
sensation but rather a sensation of colorless light. If, now, 
the colored light is gradually made to approach the center 
of clear vision where the cones predominate, its color quality 
will become more and more obvious, until, finally, at the 
center of clear vision it will be clearly seen. We may state 
this result in general form by saying that the center of clear 
vision is also the center of color vision, while the areas at 
the extreme periphery of the retina are totally color blind. 
The areas intermediate between the extreme periphery of 
the retina and the center of clear vision are partially color 
blind ; that is, they respond to a limited number of colors. 
This limitation of ability to respond to colors is offset in 
the rods by a distinct advantage on the side of susceptibility 
to slight changes in colorless light. An observer very fre- 
quently has the experience early in the evening of seeing a 
faint star in the outer edge of the field of vision, and finds 
the moment he turns to look directly at the star that it is 
impossible to see it. The periphery of the retina was suffi- 
ciently sensitive to the slight illumination to make possible 
a sensation from the faint star, whereas the center of the 
retina was incapable of responding to this slight illumina- 
tion. The significance of this differentiation of the retina in 
the development of the animal kingdom is evident. The 
periphery of the retina and the extreme edges of the field 
of vision do not have the same significance for the animal 


as the center. It is more advantageous that the animal should 
be able to concentrate its highest forms of nervous activity 
upon a limited area. On the other hand, it is important that 
the outer regions of the retina should be sensitive in such 
a way as to give immediate warning of any changes in illu- 
mination, for changes in illumination mean movement, pos- 
sibly the approach of danger, and this should be recognized 
sufficiently to warn the observer. If, then, it is desirable to 
give the object stricter attention, the eye can be turned so as 
to bring the image upon the center of clear vision. 

Color blindness. The differentiation between the different 
parts of the retina, which has just been described as charac- 
teristic of the normal retina, does not always appear. There 
are certain persons whose eyes are not fully responsive 
to colors ; these persons have at the center of the retina a 
condition similar, at least so far as color processes are con- 
cerned, to that which appears toward the periphery of the 
normal retina. This inability to respond to different color 
stimulations may in some cases be complete, so that the 
individual sees the world as a normal individual sees an 
engraving ; that is, as if it were made up only of differences 
in light and shade without the qualitative differences which 
we describe as color differences. A much larger number 
of individuals have a partial deficiency, analogous to that 
which appears in the intermediate zones of the normal 
retina. The various forms of partial color blindness are 
extremely difficult to define with precision, for the simple 
reason that the color sensations of the partially color-blind 
individual constitute his world of color sensations. He 
usually has no means of comparing his experiences with 
those of the normal individual. His efforts to describe his 
own experiences to a normal individual are complicated 
by the necessity of using terms devised for the normal 
individual rather than for his own peculiar experiences. 
Fortunately for science, there have been a few cases in 


which the same person has been able to observe directly 
both the normal color sensations and the partially color- 
blind series. The defect in such individuals appears only 
in one eye, while the other eye is of the normal type. It 
has, furthermore, been possible by certain methods of com- 
paring color mixtures to make an analysis of other cases of 
color blindness. The net result of these investigations has 
been to show that the color series of a partially color-blind 
individual is of a simpler type than that of the normal in- 
dividual with a fully developed retina. One very common 
form of partial color blindness, known as " red-green blind- 
ness/' has been thoroughly investigated. The following 
table shows the comparison between the normal color system 
and the two types of red-green blindness, which have been 
worked out : 





The red end of the spec- 


trum short ; what is seen 

is gray, or unsaturated 



Unsaturated yellow 

Unsaturated yellow 


Unsaturated yellow 

Unsaturated yellow 



Gray, or unsaturated yellow 







Such facts as are shown in this table and in the cases 
of total color blindness emphasize the intimacy of the rela- 
tion between retinal development and the development of 
experience. They make it clear that the number of sensa- 
tion qualities which an observer can distinguish depends 
not on the number of physical processes in the outer 
world but on the number of physiological processes which 
are aroused in the nervous system by the various kinds of 
physical energy. 


Color-mixing. Another group of facts closely related to 
those discussed above are the facts of color-mixing. If a 
given point on the retina is stimulated at the same time by 
two or more rays of differently colored light, the chemical 
process set up cannot be the process which is appropriate 
to either color acting alone. Experience shows that the 
process is a compromise between the processes which would 
have resulted if each ray had acted alone. Thus, if at the 
same moment a ray of red light and a ray of yellow light 
fall upon a single cone, the result is that the observer sees 
orange, which corresponds in quality to the color lying in 
the spectral series intermediate between red and yellow. If 
instead of merely using red and yellow we use red, yellow, 
and blue at the same time, we find, by observing the result- 
ant sensation, that a compromise between the three chemical 
tendencies in the cone is very different from any one of the 
processes taken alone. Indeed, in such a case the retina 
is not capable of giving a compromise color process, but 
falls back into the process which the study of color blindness 
shows to be the most primitive form of chemical activity; 
namely, the chemical process corresponding to gray, which 
we found as the only process in the eye of the totally color- 
blind person and in the periphery of the normal retina. 
When all the colors of the spectrum fall at one time on a 
cone, as in full daylight, the result is a sensation of pure 
brightness or white. 

If a red ray is mixed with a blue ray, a unique compromise 
process results, which is not directly related to any of the 
simple colors of nature ; namely, the process which gives 
rise to a purple sensation. Purple is a color quality which 
can be explained only in terms of the retinal process. Red 
and blue, which are the physical facts conditioning the ex- 
perience of purple, are at the extreme ends of the physical 
spectral series, yet they cause in the retina a single process 
which gives the sensation quality purple. This goes to show 


that the retinal processes for red and blue are closely related 
in character, in spite of the great difference in the respective 
rates of vibration in the physical processes which excite 
these retinal processes. The color circle, which was described 
in an earlier paragraph, is therefore not to be explained as 
a physical circle but as a circle of retinal processes and 
corresponding experiences. Indeed, it may be said in gen- 
eral that the laws of color-mixing are primarily laws of retinal 
behavior v rather than laws of the physical world. The fact 
that all the colors of the spectrum when mixed together 
produce gray is, as has been pointed out a number of times, 
a physiological fact and a fact of experience rather than a 
fact of physical vibrations. 

The principles of color mixtures were worked out first by 
physicists and have furnished a basis for most of the theories 
of color vision. Briefly stated, the general principles of 
color-mixing are as follows : When two colors near each 
other in the spectral series enter the eye at the same time, 
there results a sensation and a retinal process which is inter- 
mediate to those demanded by the two colors when they act 
alone upon the retina. This intermediate process is not the 
same as that which would result from stimulation of the 
retina by the intermediate pure color, for the sensation is 
not as fully saturated as it would be if it had resulted from 
the action of a pure color. As the distance between the two 
colors of the mixture is gradually increased, the chromatic 
quality of the resultant grows less and less marked, until 
finally the sensation is of the simplest possible type ; namely, 
the sensation gray. This shows that the retina is forced 
by certain mixtures of very different colors to return to the 
simple undifferentiated form of activity which characterized 
it before the differentiation into chromatic qualities began. 
Two colors which are opposed to each other in such a way 
that they give when mixed no color whatsoever, but merely 
the sensation gray, are known as complementary colors. 


If the distance in the color circle between two colors which 
enter into a mixture is greater than that required for the 
complementary effect, the resulting color will be some shade 
of purple. If purple is introduced in the color circle, there 
is no shade of color which docs not have its complement. 
The color circle shown in Fig. 23 may be made, therefore, 
the basis for discussion of complementary pairs, provided the 
arrangements of the colors opposite each other are made 
with this end in view. If more than two colors are mixed, 
the total result will be the sum of the partial effects and 
can be foreseen by considering the partial processes as if 
they occurred successively. 

Pigment-mixing subject to physical law. It may be well 
to call explicit attention to the fact that the statements here 
made regarding color mixtures do not apply to mixtures 
of pigments. The mixture of pigments is a physical fact, 
not a physiological process. The action of pigment on light 
is to absorb certain rays and reflect others. Mixtures of 
pigments affect light in a complex way, and hence produce 
results which cannot be explained by merely inspecting the 
separate pigments. 

A single case of pigment-mixing may be taken as an ex- 
ample. Thus, if yellow and blue pigments are mixed, they 
produce an impression of green. This result is due to the 
fact that the yellow pigment absorbs a good deal of light 
and reflects only those colors which are near it in the spectral 
series. Blue does the same. The only color which survives 
the joint absorptions of yellow and blue pigment particles is 
green, for green is reflected in a measure by both yellow 
pigment particles and by blue. The fact that green results 
in this case calls for an explanation absolutely different 
from that which applies to the gray which results from the 
mixture of yellow and blue light. 

After-images. The consideration of certain other facts is 
necessary to complete the discussion of visual sensations. 


If light acts upon a retinal element for a given period, the 
effect will continue for a time after the external light ceases 
to act. The observer will notice what is known as an after- 
image of the light at which he has been looking. Every- 
one has doubtless observed the vivid after-images which 
result from looking at the sun or other very bright objects. 
Most of the after-images which we receive from ordinary 
objects are so faint that they are overlooked, unless special 
effort is v made to notice them and to retain them. In gen- 
eral, the experience which continues after the withdrawal of 
the external light resembles only for a very brief interval the 
sensation originally produced by the external light. So long 
as the original impression and after-image are of the same 
quality, the observer is said to have a positive after-image. 
An example of such a positive after-image can easily be 
secured by rapidly rotating a burning stick in a circle, when 
the observer will see an uninterrupted circle of light, because 
the stimulus returns to each of the points of the retina 
before the original process has had time to change. Very 
soon after the external stimulus is withdrawn, experience 
undergoes a radical change. The general principle of this 
change may be described by saying that every black changes 
to white, every white to black, and every color to its comple- 
ment. Since these changes are known from the conditions 
to be due to physiological processes rather than to external 
light, we describe the conditions for these after-images in 
the following terms : The retina tends to set up as soon as 
possible a process opposite to that which was produced by 
the original stimulus. This chemical process, opposite in 
character to that produced by the external stimulus, is due 
to the tendency of the physiological organism to restore the 
chemical substances which have been used up in the first 
process of stimulation. The experience of the observer fol- 
lows, during this process of recuperation, the retinal activity 
rather than the external physical fact. Thus, after looking 


for a time at a brilliant red light, the observer sees very 
soon after the light is withdrawn a colored area of like 
spatial form and extent as the original but of a quality ex- 
actly complementary to the red ; namely, blue-green. In like 
fashion, the negative after-image of a blue surface is -yellow. 
If the stimulating surface is black and white or gray rather 
than colored, the negative after-image will be of such a 
character that what was bright in the original image will ap- 
pear dark in the after-image, and, conversely, what was dark 
in the original image will appear white in the after-image. 

Contrasts. After-effects in the retina very frequently 
operate to modify the retinal processes produced by subse- 
quent light stimulations. For example, let an observer who 
has been looking steadily at a bright red light for a time 
and has a strong tendency toward a green after-image look 
at a blue surface ; the blue surface will not be seen in its 
normal color, but will be seen as a mixture of blue and 
green, the green being contributed in this case by the after- 
image process in the retina. The mixtures between after- 
effects and color stimulations here under discussion give 
rise to many forms of color contrast. In view of the con- 
tinual movement of the eye from point to point in the 
field of vision, the observer is always carrying more or 
less marked after-effects from a given part of the field of 
vision to the neighboring parts. If, for example, a red and 
a green field are placed in close juxtaposition, and the eye 
after looking at the red surface tends to move in such a 
way as to bring a portion of the retina which has been 
stimulated by the red into a position such that it will 
be stimulated by the green light, the green sensation re- 
ceived from the summation of the external stimulation and 
the after-image will be more intense than a green sensation 
received without the preliminary stimulation from a red. 
The result is that green seems to be more saturated when 
it lies near red. In general, every color is emphasized by 


being brought into close relation with its complementary, 
and grays tend to take on colors complementary to sur- 
rounding fields. This effect appears even when no eye 
movements can be detected. There is probably a diffusion 
of contrast effects through the retina even when the eye 
fixates steadily a single point. 

The tendency of grays to take on colors may be well 
illustrated by shadows. If a field which is illuminated by a 
yellow light is interrupted by a shadow which is, in reality, 
gray, this gray shadow will take on a bluish tinge by con- 
trast with the yellow field. This fact has long been observed 
by those who reproduce the colors of nature in painting, and 
the shadows in painting will usually be found to be, not 
reproductions of the physical facts, but rather reproductions 
of the impression made upon the observer. 

Theories of color vision. It remains to add a few remarks 
concerning the less certain conclusions regarding the rela- 
tion between light sensations and external ether vibrations. 
The effort has frequently been made to describe the physi- 
ological processes in a single comprehensive formula or 
theory, which shall include all the facts. No attempt will 
here be made to review all of those theories. It will be 
enough to present one of the simplest and most sug- 
gestive, and leave it to the student to criticize and recon- 
struct it in the light of the facts discussed above and 
reviewed in the tables given below. 

Mrs. Franklin's genetic theory of processes in the retina. 
The theory which was formulated by Mrs. Franklin is as 
follows : The primitive retina of the lower animals and the 
periphery of the human retina have only one chemical 
process with which to respond to all light stimuli. This 
single chemical process, when set up through the action 
of light, arouses in the central nervous system a process 
which is the condition of a gray sensation. This is the 
original undifferentiated type of retinal activity. As the 


evolution of the retina goes forward, this original chemical 
process, which may be called the gray process, is so subdi- 
vided that colors produce certain partial phases of the 
original chemical activity. The partial chemical activities 
produce each a specialized form of nervous process and 
a specialized form of sensory experience. The breaking up 
of the gray process into special color processes begins with 
a development, first, of the partial processes which corre- 
spond on the one hand to blue, and on the other hand to 
orange or yellow, sensations. This first differentiation cor- 
responds to the wide difference between the extreme ends 
of the spectral series. The original gray process does not 
disappear with the rise of the blue and yellow processes, 
but remains as the neutral and more general form of 
response. At this stage the yellow and blue processes are 
each called out by a great variety of stimulations. Thus, 
the yellow process is aroused by red light, orange light, and 
green light, as well as by yellow light. As the development 
goes on, the yellow chemical process is subdivided into 
more highly specialized processes, corresponding to red 
and green. The result of this successive differentiation of 
process is that the highly organized retina may, when 
stimulated by the appropriate form of light vibration, re- 
spond with specialized chemical processes to red, green, 
yellow, or blue. If yellow and blue, which were the first 
forms of light to arouse differentiated processes, act at the 
same time upon the retina, the partial processes which are 
differentiated out of the gray cannot both be in action at 
once without being swallowed up in the original funda- 
mental process of gray. If red and green act together upon 
the retina, the yellow process appears as the more funda- 
mental form of chemical process. The facts of color blind- 
ness can be explained by stating that the differentiation of 
chemical processes is not complete in the color-blind eye. 
Negative and complementary after-images are due to the 



physiological instability of the partial chemical substances 
left in the retina after a process in which a colored light 
has partially disintegrated the retinal substance. Contrast 
has been included by earlier discussions under the same head 
as after-images, though by a spread of stimulation effects con- 
trasts appear where there are no immediate after-images. 

The student will see at once that many of these statements 
are hypothetical. They serve, however, to gather together the 
facts, and they give a genetic account of primitive as well 
as of present retinal conditions. The theory or hypothesis 
should be clearly distinguished from the facts, and yet it is 
evident that the facts justify us in attempting to explain the 
relation between physical processes and conscious processes 
by something which goes on in the retina. In order to keep 
the facts clearly in the foreground, it may be well to re- 
turn to a general summary of the different groups of facts 
discussed in this section. 





I. Full series of 
simple vibrations 

II. Full series of 
simple vibrations 

III. Full series of 
simple vibrations 

Highly developed retina 
with, however, a limited 
number of modes of re- 
sponse to external light 

Partially developed retina 
with a number of possibili- 
ties of response to exter- 
nal stimulation which is 
more limited than in the 
normal retina 

Retina so little developed 
as to have only one mode 
of response 

A differentiated group 
of sensation quali- 
ties including all 

Partial color blindness 

Total color blindness 







I. Series of simple 

Highly developed retina 

Limited number of 


with a limited number of 

sensation qualities, 

distinct modes of response 

constituting a series 

of distinct qualities 

II. Two simple 

Retinal response which 

Single color sensa- 

waves, closely re- 

compromises between the 

tion somewhat less 

lated in number 

two responses which 

saturated than in 

of vibrations, en- 

would have resulted had 

the simple series 

tering the eye 

the two vibrations acted 

together, thus 


making a com- 

pound wave 

III. Two simple 

Retinal response which 

A color very little 

waves, very dif- 

tends to take the simplest 

saturated, or a 

ferent in number 

and most general form of 

single purple or 

of vibrations, en- 

retinal behavior 


tering the eye 

together, thus 

making a com- 

pound wave 

IV. Large numbers 

Simple response of the rudi- 


of waves en- 

mentary type 

tering the eye 

together, thus 

making a most 

complex wave 





I. Strong light vibra- 
tion followed by 
the withdrawal of 
physical light 

Response followed by a 
continued action of the 
retina and a final reversal 
of the retinal process to 
restore the tissue to its 
normal condition 

Color sensation con- 
tinuing after exter- 
nal light and then 
changing into com- 
plementary color 



The task of defining sound sensations and of describing 
their conditions will be a comparatively simple one on the 
basis of the elaborate study already made of visual sensations. 

Physical sound. The physical stimulus which causes the 
nervous processes, which, in turn, condition auditory sensa- 
tions, consists of longitudinal air vibrations. When a vibrat- 
ing body strikes the air particles about it as it vibrates 
backward and forward, the air particles are alternately driven 
together and rebound from one another. Successive waves 
of condensation and rarefaction result, and these waves are 
carried forward in all directions until they strike some re- 
ceiving surface, such as the ear. These air vibrations can 
be defined in the same terms of rate, amplitude, and com- 
plexity as were used for the light vibrations in the preceding 
section (p. 77), although it should be noted that the form of 
vibrations is different in the two cases. 

Pitch, or tonal quality. With regard to the relation 
between sensation and external sound vibration, it is to 
be said, first, that when the objective waves are regular, 
they give rise to experiences of tone ; when the vibrations 
are irregular, the resulting sensation is one of noise. The 
rates of the regular vibrations which are recognized as tones 
are directly related to differences of pitch. Middle C on the 
piano scale has a rate of vibration of two hundred and fifty- 
six double vibrations per second. Toward the bass end of 
the scale the vibrations decrease in rapidity, while toward 
the treble they increase. The lowest rate which is ordinarily 
heard by the normal ear is about thirty-two vibrations per 
second, although rates of sixteen, or even ten, per second 
have been described by some observers as audible. At the 
upper end of the scale one can hear vibrations of thirty 
thousand to forty thousand per second. Sounds produced 
by insects are of this order. 


Intensity, or loudness. Intensity of tone varies according 
as the amplitude of vibration of the single air particles is 
great or small. 

Complexity of a regular type the source of differences in 
timbre. Ordinary sensations of tone are produced by com- 
plex waves. If two or more forms of vibration are transmitted 
to a given particle of air at the same moment, the particle 
will move in a path which is the resultant of all of the dif- 
ferent paths through which it would have moved had the 
various impulses of vibration acted upon it successively. 
When one compares a given tone from the piano with the 
tone of the same pitch from a violin, he will recognize that 
the characteristics of the tones are different, though they 
are of the same pitch. The violin string vibrates not only 
as a whole but also in certain sections, and the piano wire 
vibrates as a whole and at the same time in sections. The 
rates of vibration of the string and wire as wholes may be 
exactly the same. The sections in the two cases and the 
rates of their vibration will nearly always be different. The 
result is that any particle of air set in motion by either 
piano wire or violin string will have its main path deter- 
mined by the vibration of the whole wire or string, while 
the minor details of vibration will be determined by the 
vibrations of the sections of the wire or string. The phase 
of tonal quality thus determined by the complex of minor 
vibrations is known as timbre. The main, or fundamental, 
tone is modified by the minor higher tones, or overtones as 
they are called. Tones of the same pitch derived from vari- 
ous instruments have various timbres, just in so far as they 
have different overtones. 

Noise due to irregular vibrations. The experience of 
noise is dependent upon a form of vibration which is so 
complex as to be highly irregular. A vague regularity ap- 
pears in most noises. We speak, accordingly, of certain 
noises as low and rumbling, and of others as high and shrill, 


but for the most part the tendency toward regularity of 
vibrations gives way in noises to a confusion of irregular 
oscillations in the air particles. 

Evolution of the ear. Turning from the physical stimulus 
to the auditory organ, we find here, as in the case of the 
eye, that by a long process of evolution there has been pro- 
duced a sensory organ which has a variety of accessory parts 
and a delicate sensory surface, which latter transforms the 
air vibrations into nervous processes. The most primitive 
ear, such as is found in the ccelenterates, consists in a sack- 
shaped opening in the side of the body. This sack-shaped 
depression, or vesicle, contains hard calcareous particles, and 
is lined by sensitive cells which are similar in their general 
appearance to the cells in the primitive eye. The whole 
organ can be easily explained by comparing it to a child's 
ordinary rattle-box. If the animal is shaken, or if any 
sound vibrations strike against the wall of the vesicle, the 
calcareous particles, or otoliths as they are called, are set 
in motion and tend to strike against the sensitive cells. The 
result is that the cells will be stimulated by each movement 
of the animal's body or by the vibrations which enter the 
vesicle. As the ear develops through the animal series 
there appear a number of accessory organs which serve to 
facilitate the reception of vibrations, and there comes to be 
a division between the two original functions of the ear ; 
namely, that of sensory response to the movements of 
the body as a whole, and that of response to vibrations 
from the water or air. 

The human ear, pinna, and meatus. After this brief 
reference to the primitive ear we may turn immediately to 
a description of the human ear. The outer cartilaginous 
organ, known as the pinna, has in man very little function. 
It serves in a rudimentary way to concentrate the sound 
waves and direct them toward the inner ear. The long 
funnel-shaped pinna of a horse's ear serves a function which 



has been lost in the process of evolution. By moving its 
ear the horse collects sounds from different directions, and 
thus becomes very acutely sensitive to sound and at the 
same time recognizes the direction from which the sound 
comes. But the horse loses fine qualitative shades of sound 

FIG. 28. Diagrammatic section showing the structure of the ear 

P, external pinna ; JEAf, external meatus ; T, tympanic membrane ; /, internal 
meatus, or tympanic cavity. Extending from the tympanic membrane to the inner 
ear there are three bones constituting the chain of ossicles : malleus, incus, and 
stapes. ET, Eustachian tube, passing from the internal meatus to the cavity of 
the throat; SC, one of the three semicircular canals; AN, the auditory nerve, 
which divides into four parts as indicated in the figure, one branch connecting with 
the semicircular canals, two with the parts of the vestibule, and the fourth with the 
core of the cochlea, C. The canals of the cochlea are indicated in general outline ; 
for details see Fig. 30. The vestibule is the general region lying between the canals 
and the cochlea. (Modified from Czermak) 

because the funnel modifies in some measure the form of 
the air vibrations. The human ear has so evolved that it 
interferes little with quality. This shows that the sensfe of 
hearing in man is not a locating sense but a sense devoted 
to the finest discriminations in quality. The evolution of the 
ear is undoubtedly related to the evolution of speech. 


The cylindrical canal which connects the surface of the 
body with the inner cavities of the ear is known as the ex- 
ternal meatus. This canal is liberally supplied with protective 
bristles, and with secretory glands which tend to protect the 
ear from all foreign particles, and it is curved in shape so 
that nothing but very small, slender objects can penetrate 
to the inner parts of the ear. 

Nature has a relatively easy problem of protection of deli- 
cate organs in the case of the ear because air vibrations can 
be conducted along a narrow passage. In the case of the 
eye, the organ must lie exposed on the surface of the body. 
Nature has put a ring of bony structures around the eye, 
but the protection of the ear is much more complete. 

The tympanic membrane. The inner end of the external 
meatus is closed by means of a circular membrane, known 
as the tympanic membrane. This tympanic membrane is a 
composite membrane made up of circular and radial fibers. 
It is slightly depressed in the middle so as to be somewhat 
funnel-shaped and is loaded by being connected on its inner 
surface with a small bone, known because of its shape as 
the malleus, or hammer. The malleus is controlled by a 
small muscle, known as the tensor tympani. When this 
muscle is contracted it draws the malleus inward, and with 
the malleus the tympanic membrane, thus increasing the 
tension of the membrane and emphasizing its funnel-shaped 
form. The adjustments of the tympanic membrane, as well 
as its shape, are of importance in giving the ear the largest 
possible range of ability to receive sound vibrations. No 
artificially constructed diaphragm, such as those employed 
in the phonograph or telephone, is capable of as wide a 
range of response to tones as is the adjustable, complex 
diaphragm in the ear. 

Air chamber on inner side of the tympanic membrane. 
In the functioning of the tympanic membrane a difficult 
mechanical problem arises, because the air pressure in the 


external world is constantly undergoing changes. With every 
change in the barometric pressure there would be an inter- 
ference with the action of the tympanic membrane, if the 
spaces behind this membrane were air-tight. Nature has, 
accordingly, provided on the inner side of the tympanic 
membrane an air chamber communicating with the atmos- 
phere so that any change in atmospheric pressure will result 
in an equal change in the pressure on both sides of the 
tympanic membrane. This air chamber on the inner side 
of the tympanic membrane is known as the internal meatus, 
or tympanic cavity. It consists of an irregular cavity in the 
bone, which is in communication with the throat by means 
of a small canal, known as the Eustachian tube. The wall 
of the Eustachian tube is flexible, so that it collapses except 
when a current of air is forced through it by a change in 
pressure, either in the internal meatus or in the external 
atmosphere. For this reason, the ordinary voice vibrations 
which arise in the throat are not communicated directly to 
the internal meatus. 

Chain of ossicles. Since there is an air chamber on the 
inner side of the tympanic membrane, there must be some 
means of carrying the sound vibrations received on the tym- 
panic membrane across this cavity to the inner ear. The 
means for transmitting the vibrations received by the tym- 
panic membrane consist of a chain of three small bones, 
known as the chain of ossicles. The first of these ossicles 
has been mentioned ; it is the malleus, or hammer, which 
is attached by its long arm to the middle of the tympanic 
membrane. The head of the malleus articulates with the 
surface of the second bone, which is known as the incus 
because of its anvil-shaped appearance. One of the branches 
of the incus articulates in turn with the third bone, known 
as the stapes, or stirrup. Any vibration received by the tym- 
panic membrane is thus communicated to the stirrup. The 
stirrup fits into an oval opening, known as the fenestra 


ovalis, which leads into the inner ear. The stapes is con- 
nected with the walls of this fenestra ovalis by means of 
a membrane, so that it constitutes a tight-fitting piston 
which can move backward and forward in the fenestra 
ovalis. Beyond the oval window the inner ear is filled in 
all of its parts with lymphatic fluid. Sound vibrations, 
which are originally vibrations of air particles, are thus 
transformed by the mechanism described into vibrations in 
the lymphatic fluid which fills the inner ear. 

The inner ear. The inner ear is divided into three prin- 
cipal parts : vestibule, semicircular canals, and cochlea. The 
vestibule is an irregular ovoid cavity about one fifth of an 
inch in diameter, which opens on the one side into the snail- 
shell-shaped cavity, known as the cochlea, and on the other 
into a system of slender canals, known as the semicircular 
canals. The vestibule itself is divided into two parts, known 
as the saccule and utricle. 

The semicircular canals. The semicircular canals are not 
organs of hearing. They are organs which have taken up 
in the process of evolution that function of the primitive 
ear which was concerned with response to the grosser move- 
ments of the animal's whole body. There are three of these 
canals, and they lie in such positions that each one occupies 
a different plane in space. Any change in the position of 
the head, or of the body as a whole, will cause a redistri- 
bution of the pressure within the system of canals, and this 
change in pressure affects the nerve cells which are distrib- 
uted in the wall of the enlarged portion, or ampulla, of 
each canal. The whole system of canals serves as an organ 
of equilibration. The sensory stimulations which come from 
this organ do not give rise in developed human beings to 
clearly differentiated sensations. The result is that the ordi- 
nary observer does not know that he has a special sense 
organ of equilibration. The stimulations are for the most 
part taken up by the lower centers of the nervous system, 



FIG. 29. Diagrammatic 

section of the sensory 

cells in the vestibule 

The receiving cells are 
situated on the surface, as 
represented by S. These 
receiving cells are sur- 
rounded by supporting 
cells, as indicated at A. 
The nerve fiber is distrib- 
uted among the receiving 
cells. The true sensory cell 
at G is in the ganglion, 
rather than directly at the 
surface. This sensory cell 
sends its second fiber in- 
ward to the central nervous 
system, represented by C. 
(After Herrick) 

where they are distributed to the mus- 
cles which keep the body erect ; they 
probably never reach the higher regions 
except in company with a great mass 
of other excitations, such as touch sen- 
sations from the soles of the feet and 
muscle sensations from the neck and 
trunk. When they become excessively 
intense they give rise to the experience 
of dizziness. In some cases the indirect 
effects of their action come into con- 
sciousness. When the reflex muscular 
adjustment carried out by the lower 
centers is unusual, as when one de- 
scends suddenly in an elevator, the 
muscular reactions, rather than the pri- 
mary sensory stimulation, give rise to 
a clearly recognizable experience. The 
observer feels an unusual tension in 
his abdominal muscles or muscles of 
some other part of the body. 

The cochlea and sensory areas in the 
vestibule. Turning from the semicir- 
cular canals to the other canal leading 
out of the vestibule, namely the coch- 
lea, we find here the organs which 
are concerned in the reception of tonal 
stimulations. It is not clearly known 
whether noise stimulations are received 
in the cochlea or not. The probabili- 
ties are that noise stimulations affect 
certain cells constituting sensory areas 
in the wall of the vestibule. At all 
events, it is true that there are cells 
situated in the wall of the vestibule 



which seem to be suited to the reception of simple stimuli 
(see Fig. 29). The vestibule is the direct descendant of 
the primitive vesicle. This fact would seem to argue in 
favor of the view that noise stimulations, which are undif- 
ferentiated and probably earlier than tonal stimulations, 
affect these cells in the vestibule. Whatever may be true 
of noise, it is certain that the tonal 
excitations are received through the 
complicated structures which have 
been developed, and appear in the 
cochlea. The cochlea is a highly 
developed organ, richly supplied 
with cells and fibers for the recep- 
tion of a great number of different 
Stimulations. It consists of a double 
spiral canal, which winds around 
two and a half times. The winding 
of this canal is merely an anatomi- 
cal device for compressing the 
whole organ into as small a space The P arts are clear] y marked in 

... ^t . , . , . the figure. Special attention 

as pOSSlble. 1 he Canal, WhlCh IS should be given to the basilar 

Cylindrical in form, is divided into membrane and the organ of 

. , , MI- Corti situated upon it. The 

three parts, the scala vestibuh, 
the scala tympani, and the ductus 
cochlearis. This division can best 
be seen by making a section across 
the cylindrical passage. Fig. 30 
shows such a section with the division. The scala tympani 
is partially separated from the rest of the cochlea by a bony 
shelf which extends for some distance into the canal. The 
division is completed by an important membrane. This 
membrane, known as the basilar membrane, is made up of 
a series of fibers which differ in length as the membrane 
passes from the lower to the upper extremity of the canal. 
At its lower extremity the fibers are short, and at the 

FIG. 30. The structure in the 
cochlea as seen when a trans- 
verse section is made across 
the canal 

nerve fibers are distributed 
among the cells of the organ 
of Corti from the ganglion in 
a manner similar to that repre- 
sented for the vestibular cells in 
Fig. 29. (After Herrick) 


upper end of the canal they are about twelve times as long. 
Helmholtz, the great German physicist, called attention to 
the striking similarity between the structure of the basilar 
membrane and the system of strings of a musical instrument 
capable of giving a variety of different tones. He also ad- 
vanced the hypothesis that the fibers of the membrane are 
so related to external tones that a given fiber is set in 
vibration by each particular rate of vibration. It is a well- 
known principle of physical science that any fiber or rod 
will vibrate sympathetically with a tone which has the same 
rate as it would assume itself, if it were set in vibration by 
some other cause. This principle is known as the principle 
of sympathetic resonance. The basilar membrane is so situ- 
ated that the vibrations which enter the inner ear through 
the fenestra ovalis reach it by passing up the scala vestibuli 
and the ductus cochlearis. The scala tympani is a canal 
which carries back the vibrations after they have acted on 
the basilar membrane. It is connected at the upper end of 
the cochlea with the scala vestibuli and serves to conduct 
away the vibrations rather than allow them to be reflected 
back into the vestibule ; for its lower end does not open into 
the vestibule, but communicates through an opening, known 
as the fenestra rotunda, with the internal meatus. The 
basilar membrane thus stands in the direct path of the vibra- 
tions, and it is, probably, the organ which takes up the 
vibrations through sympathetic resonance and makes them 
effective in exciting the sensory cells. 

Sensory cells in the cochlea. A system of receiving 
cells, analogous to the rods and cones in the eye, is placed 
directly on the basilar membrane. At any given point they 
form an arch extending across the membrane, and, there- 
fore, are capable of taking up any vibration which sets the 
fibers of the membrane in motion. The arch of cells is 
shown in Fig. 30 and is known, from the physiologist who 
first described it, as the organ of Corti. Among the cells 


that constitute the organ of Corti there are distributed nerve 
fibers which come from auditory ganglion or true sensory 
nerve cells situated in a cavity in the bony core of the coch- 
lea. Whenever the cells of Corti are set in vibration, they 
excite the fibers. The external air wave is thus transformed 
in the organ of Corti into a nervous process. 

Contrast between auditory and visual processes. It is to 
be noted that the transformation is of a distinctly different 
type from that which takes place in the eye. In the eye 
the physical stimulus produces a chemical activity in the 
rods and cones. In the case of the ear the stimulus con- 
tinues in the form of vibrations until it produces its final 
effect upon the nerve cells. There is a less fundamental 
.change in the character of the stimulus as we pass from the 
external world to the nervous process in the ear than there 
is in the corresponding transition in the eye. This fact 
shows itself most clearly when we come to deal with com- 
pound sound vibrations. It makes no difference how many 
tones are sounded before the tympanic membrane, the com- 
plex vibration will be faithfully transmitted by the chain of 
ossicles and the other accessory organs and will, at all 
points in its transmission, be a detailed reproduction of the 
total complex of sound impulses which gave rise to it. 
Furthermore, it is shown by an examination of sensory 
experience that there must be a separate sensory process 
for each component of the tonal complex. If an observer 
listens to a tonal complex, such as an orchestra, the sensory 
excitations do not fuse as do the chemical processes result- 
ing from a number of colors which act upon the retina 
together. Each tone in the complex retains its independent 
value for experience. It was this fact, together with the 
form of the basilar membrane, which led Helmholtz to sug- 
gest his hypothesis. Whether that particular hypothesis is 
true or not, we may confidently assert that the different 
parts of the organ of Corti are specialized in some way or 


other, so that each rate of external vibration, whether it 
reaches the cochlea alone or as part of a complex of vibra- 
tions, excites a particular part of the sensory organ and so 
gives rise to a distinct sensory process. The ear is thus 
seen to be an analyzing sense capable of carrying to con- 
sciousness at one and the same moment a vast complex of 
sound. There is nothing in auditory sensation to corre- 
spond to white among the retinal sensations unless it be 
mere noise. But even here there is a fundamental differ- 
ence, because the various elements of a noise can be heard 
separately, especially if some of the elements have a tonal 
character. For example, the ear has no difficulty in hearing 
at the same time the noise produced by a train and the 
sounds produced by the human voice. 

Beats, difference tones. There are certain special cases of 
wx.ynplex air vibration which should be mentioned in this 
discussion of sensations. If two closely related tones are 
sounded together, they will reenforce the vibration of the 
air particles which they affect so long as their phases are 
alike, but the moment their phases come into such a relation 
that one tends to set the air particle vibrating in a given 
direction and the other tends to set the same air particle 
vibrating in the opposite direction, they will partially counter- 
act each other in such a way as to keep the air particle for 
a moment in a state of equilibrium. Fig. 31 represents, 
in the form of a water wave, two vibrations which at the 
outset cooperate in giving a larger wave. As one lags 
slightly behind the other, they come later to counteract each 
other in such a way that no vibration takes place, as shown 
at M. The result of such a combination of tones, which is 
a purely physical affair, is that the observer receives not 
only the two primary vibrations but also a series of rapid 
variations in intensity, which succession of intensities fuses 
into a new impression. The observer therefore hears, in 
addition to the two fundamental tones, an alternate rising 


and falling in the loudness of the sound, which fluctuation 
gives rise to experiences known as beats. If these beats 
are slow enough to be distinguishable, they will be recog- 
nized as quite distinct from the tones. If, on the other 
hand, they become too numerous to be separately apprehended, 
they may sometimes be heard as an additional tone, when 
they are designated as difference tones. For example, if 
two tones, c and g y are sounded together, these tones having 
vibrations at the rates of 256 and 384 vibrations per second, 
the result will be a complex in which both c and g will be dis- 
tinctly heard ; but there will also be heard a third tone, the 


FIG. 31. Diagram to represent the formation of beats 

The two curves represented by the light line and the dotted line begin together, 
showing the same phase at the same time. The wave motion represented by the 
dotted line is somewhat more rapid than that represented by the full line ; conse- 
quently, the relation of the two waves changes so that in the region M the two are 
in opposite phases. The heavy line indicates the results of the combination of the 
two waves. a t , e, t/, e, f, g> h indicate the strong curve which results from the 
reenforcing influence of the two wave motions. M indicates the result of the coun- 
teracting influence of the two. (After Ebbinghaus) 

number of vibrations of which equals the difference between 
the number of vibrations of c and g. That is, the difference 
tone in this case will be a tone of 128 vibrations per second. 
Summation tones. Again, there are complexities in the 
tonal experience such that often tones are heard in a tonal 
complex which, in number of vibrations, are equal to the 
sum of the two fundamentals. Such tones are known as 
summation tones. They do not seem to be purely physical 
facts, explicable in terms of the physical effect upon the air 
particles, for they cannot, in all cases, be reenforced by physi- 
cal resonators (the apparatus which is commonly used in the 
detection of single tones in tonal complexes). Summation 


tones seem rather to be due to certain physiological Sloe- 
esses, perhaps to interferences of the vibration processes 
in the basilar membrane or to secondary vibrations in the 
bony walls of the cochlea. In ordinary experiences differ- 
ence tones and summation tones play no important part, 
but the result of these tones upon harmonies and discords 
in music is a matter of some importance and one which 
has been made the subject of careful examination. 

Harmony not a matter of sensation. By these discussions 
of tonal sensations and their combinations we have been 
led to the point where it would be appropriate to take up 
the matter of harmony. Certain tones, when sounded to- 
gether, give the observer an experience which is not merely 
that of tones sounding together, but is also an experience 
of the smooth fitting together of these tones, while other 
combinations give the observer a distinct impression of jar 
or discord. The effort has often been made to explain 
harmony and discord as due to beats and like facts ; that is, 
to certain simple processes in the organ of sense. We shall 
dismiss the matter in a somewhat dogmatic fashion by say- 
ing that such explanations of harmony, by processes of a 
purely sensory type, are not satisfactory. There is probably 
a close relation between recognition of harmony and motor 
processes, such as those of the vocal cords and those of the 
inner organs which, as will be seen later, are aroused during 
emotional experiences. f < t ^V*> ;N ^ 8 > ^ C ^ QS ' ? 

Absence ofl after-images in auditory sensations. Before 
closing the discussion of tonal sensations it should be noted 
that the nature of the auditory sensory process is such that 
contrast and after-effects do not appear to any great extent 
in tonal or noise sensations. The process in the nerve cells 
terminates as soon as the external vibration ceases. This 
characteristic of sound sensations explains why it is that 
these sensations can be, used in musical compositions. A 
succession of 'colors, given in anything like the same 


reapon as a succession of tones in music, would produce a 
hazy blur of after-effects. 

Tone deafness. Cases of tonal deafness, or inability to 
receive certain tones, have been described. A person capable 
of the usual tonal discriminations in many parts of the 
scale is quite unable to distinguish tones in a certain limited 
part of the scale or at one end of the scale. This deficiency 
is undoubtedly related to some lack of normal functioning 
in a given region of the basilar membrane, or organ of 
Corti. In old age a person may also show increasing 
deficiency in ability to hear very high tones. 


Without attempting to summarize all that has been said in the 
discussions of tonal sensations, it may be advantageous to prepare 
a table which may be used for the purposes of comparison with 
the earlier tables referring to visual sensations. 




Series of air vibrations 

No physiological excitation 

No sensation 

below 10 per second 

Continuous series of 

A very large number of dif- 

Large number of sen- 

changes in rate of 

ferent processes in the 

sations ranging in 

air vibration from 

basilar membrane and 

series from lowest 

32 per second to 

organ of Corti ; the num- 

to highest pitch 

30,000 or 40,000 

ber being, however, less 

per second 

than the number of phys- 

ical processes 

Same as above 

More limited number of phys- 

Partial tone deafness 

iological processes because 

of incomplete development 

of the organ of Corti 

Complex vibrations 

Separate physiological proc- 

Recognizable com- 

ess for each component 

plex of tonal sen- 

of the complex 


Complex vibrations 

Interference of vibration in 

Summation tones not 

the physiological organs 

paralleled by objec- 

tive vibrations 




Taste and smell differentiations of a primitive chemical 
sense. Sensations of taste and smell may be considered 
together. Indeed, in the primitive forms of animal life, 
taste and smell constitute a single chemical sense. Of the 
two the sense of smell is distinctly later in its development, 
appearing as an important separate sense with the appearance 

of the air-breathing animals. 

Position of olfactory organ in 
the nasal cavity. It is unneces- 
sary here for us to consider at 
any great length the nasal cavities 
in which the olfactory cells are 
situated. These cavities are not 
true accessories to the organ of 
sense, as were the cavities in the 
ear. The organ of sense is rather 
FIG. 32. The inner cavity of accessory to the general organ of 
the nose respiration. The position of the 

The arrow A indicates the path of sensory ce H s J s suc h t h a t they are 
the air m ordinary respiration; B . J J 

indicates the path of the air when not in the direct path of the great 

the animal sniffs The olfactory re- volume o f air w hJ C h is USed in 
gion is indicated by the black area 

in the upper part of the cavity the prOCCSS of respiration. Fig. 32 

shows the area within the nasal 

cavity which is covered by olfactory cells. The arrow A in 
the figure indicates the path of the air current in ordinary 
respiration. It will be noted that in such ordinary respira- 
tion very little of the air is carried up into the upper part 
of the nasal cavity and thus brought into contact with the 
sensitive cells. If for any reason it is desirable that the 
sensitive cells should receive the full current of air which 
enters the nose, the animal must sniff the air forcibly into 
the nasal cavity, in which case it will follow the direction of 
the arrow B in the figure. 



Structure and function of the olfactory surface. The 

olfactory surface itself is made up of two kinds of cells, 
as shown in Figs. 33 and 34. There are, first, certain 
supporting cells which line the nasal 
cavity ; and second, there are distributed 
among the supporting cells true sensory 
cells, from which fibers pass inward to 
the central nervous system. The nerve 
cells in this organ are immediately on the 
surface, in such a position that particles 
brought in through the air currents come 
into direct contact with the cell body 
proper. This direct exposure of the nerve 
cells to stimulation is undoubtedly related 
to the fact that these cells are very easily 
fatigued. It is a well-recognized fact 
that an odor which is very striking at 
first soon grows less and less impressive, 
even though the stimulus may continue FIG. 33. Section show- 
in its original intensity. Furthermore, ing the different cells 
J which compose the 

the olfactory cells do not seem to be very mucous ii ning of the 

definitely specialized, and there are no nose in the olfactory 

selective organs between the external 

stimulus and the sensory organs which 

determine the effect of the stimulus on 

the nervous organs. There is, accord- [\ th T e other c r e11 * as 

b ' black. In one of these 

ingly, no clearly defined limit to the ceils the nerve fiber will 
number and variety of olfactory sensa- be seen passing directly 

J i i i out * t e ce ^' towai "d the 

tions. By way of contrast with the visual central organ 

organ, for example, there is, in the case 
of the olfactory sense, nothing which corresponds to the rods 
or cones and operates to reduce all external stimulations to 
a limited number of sensory processes. Consequently, the 
number of olfactory sensations is very large, and the effort 
to classify them is defeated by their variety. 


By the staining process, 
the special sensory cells 
are clearly distinguished 



Olfactory stimuli. With regard to the character of the 
external stimuli which affect the cells of the olfactory sur- 
face, our knowledge is somewhat limited. Minute particles 
probably detach themselves from external objects and are 
carried by the air currents during inspiration into the nasal 
cavity. These particles, or effluvia, produce a chemical effect 
upon the olfactory cells. In general, it seems to be true 
that those substances which are most fre- 
quently brought into contact with the olfactory 
surface produce the least effect, whereas new 
and unfamiliar substances produce a strong 
effect. The relation between the external 
effluvia and the olfactory processes is probably 
the outgrowth of the long evolutionary proc- 
ess, in which the sense has developed as its 
chief function the ability to warn animals of 
the presence of unfamiliar substances in the 
atmosphere. Noxious gases are, from the 
nature of the case, relatively uncommon, and 
the olfactory sense, in serving to warn us of 
their presence, not only shows its adaptation 
to the stimuli which are unusual but shows, 
also, the significance of the whole develop- 
ment as aimed at the preservation of the 

Smell a rudimentary sense in man. Ani- 
mals make much larger use of the sense of smell than do 
human beings. They often take advantage of the presence 
of strange effluvia in the atmosphere and react positively 
to these odors, seeking the source of the odor, if it leads 
them, for example, to food. It is to be said in this con- 
nection that the human sense of smell can be much more 
highly cultivated than is commonly the case, if attention is 
directed to these sensations in early life. Such attention aids 
discrimination, but does not change the organ itself. 

FIG. 34. Olfac- 
tory cells and 
supporting cells 
(much magni- 

The supporting 
cells are here 
shown to be larger 
than the true 
sensory cell and 
somewhat differ- 
ent in form 



Taste qualities and taste organs specialized. Turning from 
smell to taste, we notice first that the qualities of taste sen- 
sation are more easily reduced to a classified list. The quali- 
ties most constantly recurring are bitter, sweet, sour, and 
saline. If we add to the list al- 
kaline and metallic, which may 
be compounds, it is possible to 
classify all taste experiences as 
belonging under the one or the 
other of the six classes, or as 
compounds of these. This re- 
duction of all tastes to a few 
qualities leads one to look for 
structures in the organ of taste 
which shall explain the reduc- 
tion of the physical manifold 
to a small number of sensory 
qualities. The study of the 
organs of taste shows that they 
are specialized structures, prob- 
ably of a selective character. 

Organs of taste. The taste 
organs are distributed through- 
out the mouth and throat. They 
appear in greatest abundance 
on the papillae of the tongue. 

FIG. 35. The depression between 
the sides of two papilla? on the 
surface of the tongue 

Fig. 35 Shows a magnified Sec- Liquids may pass down into this open- 

through the Side Of One Of m g- On its sides are taste bulbs. Their 
,11 11 A , , . number and distribution are indicated 

the large papillae. At certain in the figure 

points in the walls of the papilla 

there can be distinguished groups of cells clustered in bulb- 
shaped organs. These are known as the taste bulbs. Each 
bulb is made up of a number of cells grouped about its wall 
and constituting a minute pear-shaped organ (Fig. 36). 
Among these cells in the bulb are distributed tactual nerve 



fibers and special taste fibers (Fig. 37), which come from 
nerve cells located in the immediate vicinity of the medulla. 
The cells of the taste bulb are chemically affected by certain 
fluids which act upon them, and the chemical processes set 
up within the peripheral cells are transmitted first to the nerve 
fibers, and through these to the nerve cells, and, finally, from 

the receiving nerve cells 
to the central nervous sys- 
tem. Probably not all the 
cells in the taste bulbs act 
equally in receiving taste 
stimulations. Some of the 
cells in the bulbs seem to 
be specialized for the taste 
function, while others play 
the part of supporting 
cells. The peripheral or- 
gans are not true nerve 
cells, as were the receiv- 
ing cells in the olfactory 
organs ; they are interme- 
diate between the sensory 
fibers and the outer world. 
Their function is, un- 
doubtedly, selective. This 
accounts for the more 
definite and independent 
character of the taste quali- 
ties as compared with odors. The selective character of the 
taste cells is strikingly shown by the fact that not all taste 
bulbs receive with equal facility the various taste stimula- 
tions. Thus, the cells in the back part of the tongue are 
much more sensitive to stimulation from bitter substances. 
Cells in the front part of the tongue respond more readily 
to sweet solutions. On the sides of the tongue the areas 

FIG. 36. A diagrammatic section of a 

single taste bulb showing the character 

of the different cells 

The cells marked n are the special sensory 
cells. The cells marked ss are supporting 
cells. It will be noticed that the cells consti- 
tuting the bulb are somewhat larger than those 
which form the general surrounding tissue 



are especially sensitive to sour and saline stimulations. To 
be sure, the localization is not absolute, especially for sour 
and saline, but it is very far in advance of anything found 
in the olfactory surface. 

Gustatory stimuli. The substances which act upon these 
taste bulbs must be in liquid form. If one dries the tongue 
thoroughly, the substances 
which would otherwise pro- 
duce taste impressions can 
be pressed against the 
tongue without producing 
any effect. For example, 
a piece of dry salt placed 
upon the dry surface of 
the tongue will not give 

rise to any taste sensation. [/ A a 


D. SENSATIONS OF TOUCH FIG. 37, A diagrammatic sketch show- 
ing two neighboring taste bulbs 

Organs of touch. The 
group of sensations popu- 
larly classified under the 
sense of touch might very 
properly have been con- 
sidered at the beginning 
of this chapter, for touch 
is the human sense which 

is most closely allied in character and in the structure of its 
organs to the primitive senses of the lower animals. Indeed, 
the surface of the body is a relatively undifferentiated mass 
of protective and sensory cells, which are open to stimula- 
tions of all kinds and capable of responding in some degree 
to almost any form of external energy. The true nerve cells 
for the sense of touch are situated in the immediate neigh- 
borhood of the spinal cord. They are primitive bipolar cells, 

The supporting cells have been removed in 
the two bulbs. The bulb on the right has 
four specialized gustatory 'cells. The network 
of fibers at the base of these cells shows the 
mode of distribution of the gustatory nerve 
fibers. In the bulb on the left and in the 
intermediate tissue between the bulbs, the 
terminations of the tactile nerve fiber are 
shown. The tongue is thus seen to be an 
organ of touch as well as of taste 


as shown outside the cord in Figs. 13 and 14. The branch 
which passes out of one of these bipolar cells toward the 
surface of the body is the receiving sensory fiber. When it 
reaches the skin, it breaks up into a fine network of fibrils. 
These fibrils are distributed among the cells of the skin. 
The nerve fiber which travels inward from the receiving cell 
extends into the spinal cord. Such a fiber was described 
in the discussion of the spinal cord. It will be recalled that 
this central fiber branches so as to extend upward and 
downward through a large section of the spinal cord, send- 
ing out at various levels collateral branches which transmit 
the stimulation to the motor cells at the different levels of 
the cord or transmit the stimulation to the higher nervous 

Differentiation of the tactual fibers; temperature spots. 
The sensory fibers which pass to various parts of the surface 
of the body seem to be differentiated in their functions to 
some extent in spite of the uniformity of their structure. 
For, while it is probably true that there is no region on the 
surface of the body which is not susceptible to stimulation 
in some degree by all forms of external energy, provided 
the energy is strong enough, yet it is certain that there are 
regions capable of responding easily to slight changes in 
pressure and temperature. Indeed, there are areas which 
show special susceptibility to pressure, and others which are 
especially sensitive to temperature. The specialized areas are 
usually points or, at most, limited areas. The most striking 
demonstration of this differentiation of the skin can be se- 
cured by taking a metallic point which has been reduced some- 
what in temperature and passing this point slowly across the 
skin. At intervals the point will be recognized as distinctly 
cold, while on other parts of the skin it will be recognized 
merely as an external pressure without temperature quality. 
Those areas where the point is recognized as distinctly cold 
have been designated cold spots. 


Pressure spots. A second type of specialized points on the 
surface of the skin includes those points which are specially 
susceptible to stimulations of pressure. If one applies a fine 
hair to points on the skin, it will be found that there are cer- 
tain points at which the pressure will be recognized, while 
there are other points from which no sensation will arise. 
Those points which respond to the slightest stimulation are 
called pressure spots. The number of pressure spots discov- 
ered in any special region will depend, of course, upon the 
intensity of the pressure exerted by the hair, so that the term 
"pressure spot" is a relative term and depends for its exact 
definition upon the intensity of the stimulus applied to the skin. 

A part of this differentiation of sensory excitations is due 
to the structures which surround the tactual sensory fibers, 
but beyond this there is a demonstrated difference in the 
receiving fibers themselves. 

Other " spots." Heat spots and pain spots can also be 
found. The heat spots are much more diffuse and difficult 
to locate than the cold spots, but they are analogous to the 
cold spots in their response to changes in temperature stimu- 
lation. Pain spots appear in certain parts of the body and 
may, perhaps, be defined as specially sensitive pressure spots. 
Whole areas of the body surface, as, for example, the cornea 
of the eye, are so sensitive that any stimulation which is rec- 
ognized at all will be recognized with the quality of pain rather 
than that of simple pressure. There are certain reasons for 
treating pain as distinct from pressure. Thus, when a sen- 
sory nerve fiber has been injured and is gradually recovering 
its functions, pain sensibility and pressure sensibility are 
restored at different stages of the recovery. 

Relativity of temperature sense ; chemical and mechanical 
senses. One characteristic of the temperature spots is their 
change in sensitivity when stimulated for a period of time by 
any given temperature. For example, the hand which has 
grown cold from a long exposure to cold air will react to water 



of a moderate degree of temperature in such a way as to give 
rise to the sensation of warmth, while the same hand, after 

it has been exposed to 
warm air, will give sen- 
sations of cold from the 
same water. This rela- 
tivity, as it is called, of 
the temperature sense is 
due to the fact that the 
nervous processes in- 
volved are chemical proc- 
esses which, when once 
established, change the 
FIG. 38 A. Tactual end organs condition of the sensory 

A section of the cornea of the eye much magni- Organs SO that the 

fied. The small cells in the upper part of the ^ on o f J a t er stimulations 

figure show that the tissue is made up of a num- - .. u I u 

ber of small, compactly arranged cells. A nerve depends Upon DOth the 

fiber is seen distributing its branches among present Stimulation and 

these cells. This is a typical form of distribution . ... . , , . 

of the tactual fiber, which ends freely in the the Condition induced by 

surface of the body. (After Testute) p as t stimulations. Simi- 

lar facts have been noted 
in the discussion of color 
contrasts and olfactory 
fatigue. There is no 
marked relativity in the 
case of sensory proc- 
esses of hearing or of 
pressure. There is a 
basis in these differ- 
ences with regard to rel- 
FIG. 38 c. A Mis- ativity for a distinction 
between the chemical 
senses on the one hand, 
including the temperature sense, the senses of smell, taste, 
and vision, and the' mechanical senses on the other hand, 

FIG. 38 B. A Pa- 

cinian corpuscle. 

(After Testute) 

senian corpuscle. 
(After Testute) 



including those which depend upon direct excitation of the 
nerve fibers ; namely, pressure and hearing. The chemical 
senses show greater relativity and more striking after-effects 
than do the mechanical senses. 

Organs of touch at the periphery. The peripheral endings 
of tactual fibers are in some cases surrounded by special struc- 
tures ; in other cases the fibers end freely among the cells of 
the skin. A number of typical end organs are shown in 
Figs. 38-41. Some evidence has been accumulated to show 
that the differentiated qualities of 
tactual sensation are related to these 
specialized structures. Thus, there 
are certain organs which appear in 
the conjunctiva where there is no 
sensitivity for pressure, but where 
there is sensitivity for cold. This 
leads to the inference that they are 
special organs for cold. Again, cer- 
tain tactual cells seem to be espe- 
cially numerous in regions sensitive 
to pain. Pain, however, is the only 
type of sensation from certain other 
regions where the fibers end freely 
among the epithelial cells. The evidence is, therefore, not 
conclusive that the end organs in the skin are specialized; 
they may be primarily protective organs. 

Muscle sensations and organic sensations. Sensations from 
the inner organs of the body have sometimes been classified 
under the tactual sense ; sometimes they have been regarded 
as constituting separate classes. All the inner organs of the 
body have sensory nerve fibers similar to the tactual fibers 
which end in the skin. Thus, the muscles, joints, linings of 
the organs of the thoracic, and especially of the abdominal, 
regions are all supplied with sensory nerves. In discussing 
the experiences received from the limbs, it is sometimes 

Fic-39. Two Golgi-Mazzoni 
corpuscles of the type found 
by Ruffmi in the cutaneous 
connective tissue of the tip 
of the human finger 



convenient to distinguish under the name " muscle sensa- 
tions*' the experiences resulting from the excitation of the 
sensory fibers ending in the muscles. In like manner, 
sensations from the abdominal organs 
are sometimes classified as organic 
sensations. The motives for minute 

. analysis of these sensations from the 
A . , 

inner organs are not strong, because 

these sensations are relatively un- 
differentiated. In the normal course 
of life they come into experience 
with a great mass of skin sensations, 
and they never are intense except 
when they are abnormal. 


Intensity a general characteristic. 

FIG. 40. Shows the com- while it has been necessary to dis- 

plex distribution of a tactual . , . . r 

nerve fiber in the immediate cuss sensation qualities in terms of 

the relation of these qualities to vari- 

The freely ending nerve fibers OUS Organs of Sense and Various forms 

in region A directly under the of exte rnal energy, it is possible to 
treat the matter of sensation intensi- 
ties in a somewhat more general way. 
The relation of changes in the in- 
tensity of objective sounds to changes 

glandular tissues marked G in in the intensity of sound sensations 
the figure. Branches from the [ s o f essentially the same type as the 

general nerve trunk are distrib- . . . . . f 

uted, as indicated at x, about relation between the intensity of pres- 

the hair and its surrounding tis- sure stimuli and pressure Sensations, 
sues. (After Retzius) , . . . , . 

Indeed, it is in this sphere of sensa- 
tion intensities that the general methods of modern experi- 
mental investigation ,were first most fully developed. The 
early experimental investigators had the largest confidence 

vicinity of a hair 

epidermis are to be compared 
with the freely ending nerve 
fibers shown in Fig. 38 A. These 
fibers before their distribution 
in the area A form a network in 
the cutis in the area R. Around 
the shaft of the hair are certain 


that they would be able to develop general mathematical 
formulas which would define the relations between external 
stimuli and sensation intensity with a degree of comprehen- 
siveness and precision comparable to that which is attained 
in the physical sciences. As a result, they performed the most 
laborious experiments and collected a mass of data which is 
not equaled in quantity by the data relating to any other single 
sphere of psychological phenomena. 

Weber's Law. The general principle 
which was established by these investiga- 
tors is commonly known as Weber's Law. 
This law states that the increase in sen- 
sation intensity does not follow directly 
the increase in the physical stimulus. 
While the physical stimulus is increasing 
either continuously or by additions of 
small increments, the sensation increases 
in recognizable intensity only after there 
has been a certain percentage of increase 
in the intensity of the external stimulus. 
To make the matter concrete, if a certain 
intensity of light is continuously increased 
or is increased step by step by small ad- 
ditional amounts of energy, there may 
result in subjective experience no appreciable increase what- 
soever. Before a change in the intensity of the sensation can 
arise, the external light must be increased by about T ^ of 
its original intensity. Various investigators have found some- 
what different fractions ranging from j^g- or T i y to ^, but 
in any case when the fraction is determined for a given in- 
tensity of light, say one hundred candlemeters, the same 
fraction holds, at least approximately, for all other medium 
intensities. The meaning of Weber's Law can be made 
clear by considering the following negative illustration. If we 
add to a single candle the small quantity of light necessary 

FIG. 41. Tooth of 
Gobinus showing dis- 
tribution of nerve 
fiber throughout the 
canal of the tooth. 
(After Retzius) 


to increase it by yj^i an observer will be able to recognize 
the change. If, now, we add to a light of one thousand 
candlepowers the same y^ of a single candlepower, the 
effect will be absolutely unappreciable ; that is, the sensation 
in consciousness will not be modified at all. Ten candle- 
powers must be added to one thousand before an appreciable 
change takes place in the observer's experience. 

General statement of the law. The law holds in general 
for all spheres of sensation intensity. The ratio of increase 
in the different spheres of sensation differs. Thus, while 
it is r J0 for light, it is given by Wundt as } J - for pressure. 
Other fractions are reported for other spheres of sensation. 
In general, however, the relation is always of the same type. 
It has been expressed briefly in the statement, if the sen- 
sation is to increase in an arithmetical ratio, the stimulus 
must increase in a geometrical ratio. The range of applica- 
bility of this general principle is limited in each case to 
stimuli of moderate intensities. 

Mechanical explanation of Weber's Law. After the law 
has been established as a statement of an empirical fact, it 
is by no means easy to determine its value for the explana- 
tion of mental life. It probably expresses a law of nervous 
behavior which is a special case under the general mechanical 
principle, that any increase in any form of physical activity 
becomes more and more difficult as this activity reaches a 
higher level of intensity. For example, it is extremely 
difficult to add to the speed of a locomotive beyond a certain 
point. If the locomotive is moving at the rate of fifteen 
miles an hour, a moderate increase in the amount of energy 
applied to the machinery will increase the speed by a mile 
an hour. If, however, the engine is moving at the rate of 
sixty miles an hour, the amount of energy which must be 
expended to add one mile to its speed is very much greater 
than the amount which was necessary to add this same in- 
crement of speed when the engine was moving at the rate 


of fifteen miles. This mechanical principle is applicable to 
the action of the nervous system. If the external stimulus 
acting upon the sense organs is producing a certain mod- 
erate degree of chemical activity, that chemical activity can 
be intensified by a small addition to the external stimulus. 
If, however, the stimulus acting upon the nerve cells is so 
strong that it demands nearly all of the energy that the cell 
is capable of giving out, then the small addition to the 
stimulus will produce no effect. Since this is a general 
principle of all nervous behavior, it is a principle which 
appears alike in all the different spheres of sensation. 

Other views regarding Weber's Law. Other interpreta- 
tions of Weber's Law have been given in the history of 
psychology. One such interpretation, given by Fechner, 
was of a most ambitious type and was intended by its author 
to. express in exact mathematical terms the general relation 
between mind and matter. The significant fact which 
Fechner was emphasizing, that the relation between con- 
sciousness and the physical world is not direct, is abundantly 
established by considerations of a more general character 
than those which Fechner took up. We have seen in our 
earlier discussions of sensation qualities that there are many 
other phases of experience which do not parallel the physical 
facts with which they are related. The importance of Weber's 
Law as a demonstration of the indirectness of the relation 
in question is, therefore, relatively less now than it was in 
the time of Fechner, and his definite mathematical formulas 
are of no value. The whole study of sensation intensities 
was, indeed, more productive for general psychology in the 
experimental methods which it served to cultivate than in 
the contribution which it made to the content of psychology. 
The discussion of sensation intensities may, accordingly, be 
dismissed without further detail. 



All consciousness complex and selective. A man comes 
into a room and sees a piece of paper on the table. He 
walks to the table, picks up the paper, and after looking at 
it throws it down again. If we try to give a psychological 
explanation of these acts, we find ourselves adopting some 
such formula as this. The act of going to the table and 
picking up the paper is due to curiosity and an inner desire. 
Curiosity and desire are aroused by the sensory impression 
which the paper made on the man's eye. After the first 
act of picking up the paper, a new series of visual im- 
pressions fell on the retina ; these new impressions aroused 
a new series of inner processes and the act of throwing 
down the paper followed. Experience is thought of under 
this formula as a series of cycles, each beginning in a sen- 
sation and ending in an act. 

The formula is much too simple. When we consider 
carefully the first statement " sees a piece of paper/' we find 
at once that we are dealing not with a sense impression 
alone; we are dealing with a vigorous form of behavior. 
The act of looking at an object involves the turning of the 
two eyes in a very complicated way on the object and in- 
volves also the focusing of the lenses inside the eyes. Not 
only so, but looking at an object is a highly selective per- 
formance. The room into which the man came offered to 
his vision a hundred shades of color and a hundred varieties 
of brightness. Out of all these he fastened on one small 
patch. The walls of the room were quite as bright as the 



paper and very much more extensive ; they offered sensa- 
tions which in their quality and intensity would overwhelm 
the piece of paper if sense impressions alone determined 
the flow of mental life. The fact that the man looked 
at the paper rather than at the walls is the first and most 
essential fact which the psychologist must take into account 
if he would give an adequate explanation of the later act of 
picking up the paper. 

The selective character of conscious processes related to 
sensory impressions. Our common descriptions emphasize 
the active character of the processes of recognition here 
under discussion. We say the man is interested in pieces 
of paper, while he has no special interest in walls. Or we 
say that the man is trained to give attention to what is on 
the table, but is indifferent to the walls of the room. Some- 
times we go further and give the explanation of the man's 
interests and his attention by saying that he has cultivated 
certain associations or certain modes of thinking which 
determine the directions in which his mind turns. 

Such statements make it clear that psychology cannot rest 
content with the explanation that each cycle of experience 
begins with a sensory impression. By the time the mind 
receives a sensory impression the selective process has gone 
a long way ; the selective process which is involved in at- 
tending to a sense impression is itself a preliminary stage 
of no small importance. 

It will not be amiss to recall at this point one of the 
important lessons drawn from our study of the evolution of 
the organs of sense. Our organs of sense are by their very 
structure selective organs. The eye cannot respond to rays 
of light below the red or beyond the violet. The ear does 
not record sounds of the slowest rates of vibration or those 
of the highest pitch. Evidently the organism has been 
determined in its evolution by causes which are more funda- 
mental than those of mere sensation, for there has been no 


evolution of universal sense organs, but only evolution of 
organs capable of receiving certain impressions which the 
organism can use in promoting its own life. 

Selective consciousness related to behavior. The key to 
this whole matter is found in a study of bodily activities. 
Every animal is a reacting being. All its functions 'relate 
to what it can do. For example, there is a certain range of 
objects which are of such size that they can be picked up 
by the human hand or moved by human fingers. It is an 
impressive fact of biology that the range of human vision 
corresponds to this range of action. We do not have micro- 
scopic eyes like the fly. Nor, on the other hand, do we 
have distance vision like the eagle's. With our present 
organs of behavior we could not react to the minute objects 
which the fly sees, nor could we use far-sighted eyes to ad- 
vantage from our position near the ground, for even if we 
could see at great distances, we could not move fast enough 
to take advantage of our superior sight. The range of human 
vision has been determined by the range of possible human 
reactions. The impressions of the eye are of importance 
only when there is a corresponding power of action. 

Common interests and their relation to behavior. That 
action is a determining consideration in mental life will be 
clearly seen when one begins to look at ordinary experience 
with a view to finding what is back of sensations. One who 
is not interested in doing something with trees will pass 
them a thousand times and never really see them. The 
maple tree has a shape wholly different from that of the 
elm. The barks of the two are quite different. The casual 
observer passes these trees day after day and his retina 
receives the appropriate sensory impressions with their vary- 
ing characteristics, but the impressions go to waste. Let 
this observer be induced to try to draw the trees, and his 
experiences undergo a vast change. The impressions begin 
to be vivid ; they have not undergone any modification in 


their character as sensory excitations, but they have taken 
on new importance in the psychological world. The psycho- 
logical character of the impression can be described only 
by saying that the impression has been selected for attention 
or has been made vivid and distinct by virtue of the effort 
to use it. 

Another example is found in the familiar experience of 
not hearing a clock tick so long as one is absorbed in read- 
ing. When the reading is over and there are no dominating 
ideas in the rrjind, the ticking begins to be heard/ The fact 
is, of course, that the ear recorded the ticking in both cases. 
While one was reading, the nervous system was pouring its 
energy into the eyes which were looking along the printed 
lines. There was, furthermore, the general muscular reaction 
characteristic of purely visual attention, the tense breathless 
interest in the story on the printed page. The auditory im- 
pressions were absorbed into this stream of active processes 
and were lost. When the activity of reading is over and the 
body and the nervous system fall back into the miscellaneous 
activities characteristic of partial relaxation, there may be a 
turning of the head to listen and then the ticking may 
occupy the center of attention. 

One might multiply examples indefinitely. On the street 
we pay little or no attention to the people whom we are 
passing. Our one purpose in most cases is to avoid collision, 
and our attention to sensory experience is just enough to 
serve this end. The skilled cabinetmaker sees in a piece 
of furniture elements which the untrained layman would not 
notice. The hunter observes what the stranger in the woods 
overlooks. Everywhere it is behavior that determines the 
emphasis on sensory impressions. 

Study of evolution of organs of action ^s important as 
study of senses. The relation of bodily activity to mental 
processes will be more fully understood if we trace the evo- 
lution of the muscular system and its operations much as we 


traced the evolution of the organs of sense. In an earlier 
chapter the primitive muscle cells in the body wall of the 
hydra were shown in Fig. 4, and the contrast in both form 
and function between the muscle cells and the neural cells 
was pointed out. The muscle cell is large and elongated. 
It is large so that it can store up more energy than could 
be stored in a small cell, and its elongated form favors con- 
traction. Fig. 42 shows a single muscle cell of one of the 
higher animals. A muscle is made up of a mass of such 
cells. Every muscle is supplied with a nerve the ends of 
which are distributed to the cells and produce contractions 
of the muscle by discharging motor impulses into the cells. 
The phenomena of contraction are illustrated in Fig. 43. 
This process of contraction consists in an inner chemical 
change which uses up a part of the energy stored up in the 

cell body. The proc- 
esses may be com- 

^ A 1- 1.7^ i j i n pared to combustion. 

FIG. 42. A highly developed muscle cell r 

When a piece of 

wood burns, it gives off a part of the energy stored up in 
its complex chemical substances. So it is with the muscles ; 
they give out energy and have left behind certain waste 
products which may be described as the ash of combustion. 
Evolution from gross muscles to highly differentiated 
muscles. The highly specialized muscle cells of the type 
shown in Fig. 42 have been evolved from the cells which 
make up the surface of the body in such simple animals as 
the hydra. Furthermore, the muscles of the higher animals 
have in the course of evolution become differentiated into a 
large number of highly specialized groups of muscle cells. A 
single illustration will make clear the type of evolution which 
has gone on in all parts of the body. The mouth of one of 
the lower animals, such as a fish, is opened and closed by 
very simple muscles., In the higher animal forms the differ- 
entiation of muscles goes much further. The opening and 



shutting of the human mouth, for example, is not a single 
gross performance as in the fish. The muscles of the lips 
have been evolved and so highly differentiated that one side 
of the mouth can be moved, as it is in many forms of facial 
expression, quite independently of the gross opening and 
closing of the jaw, which is the only form of movement of 
which the fish is capable. 

In like manner the 
hand exhibits a high 
differentiation * of the 
muscles. When we 
study the ability of a 
human being to move 
one finger apart from 
the rest of the hand, 
we realize how far dif- 
ferentiation of the mus- 
cles has gone. 

Behavior dependent 
on nervous control. The 
highly differentiated 
muscular system of the 
human body takes on a 
greater significance for 
the student of psychol- 
ogy when it is kept in 
mind that the muscles 
are always connected 
with the nervous system and are absolutely dependent on 
the nervous system for the impulses which cause their con- 
traction. In the lowest animal forms the muscle cells had a 
general irritability, but in the process of evolution the muscle 
cells have been specialized to store up great quantities of 
energy. They do not in their later specialized stage receive 
impressions directly from the outer world. They contract 

FIG. 43. The contracted and relaxed state 
of a muscle 

The dotted lines within the muscle show the 
distribution of the nerve fiber 


only when they are excited by nervous impulses. The higher 
the animal, the more its muscles have become dependent on 
the nervous system. The result is that when the muscular 
system becomes highly differentiated there must be a parallel 
evolution of the nervous centers related to these muscles. 
There has been, accordingly, a steady evolution of the con- 
trolling nervous organs. When we study the human hand 
and its complex possibilities of adjustment or when we 
study the delicate movements of the human face, we must 
always have in mind the fact that there arc corresponding 
differentiations of the nervous system. 

Coordination as necessary counterpart of differentiation. 
There, is another consequence of this differentiation of 
the motor organs which is of importance for our study. 
The highly differentiated muscles may, indeed, contract 
each by itself in the performance of some special function 
for which it was evolved, but for the most part the special 
muscles act in systems. The individual muscle becomes 
for the purpose of the moment not a separate organ, but 
a part of a system of cooperating muscles. For example, 
the single finger may move by itself, but in many of the 
activities of life the single finger contributes its strength 
to a grasping movement which enlists all the other fingers 
and the whole hand. In a grasping movement the finger is 
not a separate organs Here, then, we have a complex situ- 
ation ; the differentiated muscles which move the finger 
must sometimes act separately, sometimes as parts of a 
combination of many muscles. In the same way the 
nervous centers must be both specialized and capable of 
entering into combination. 

Individual development in behavior. The history of indi- 
vidual development of muscular control shows how compli- 
cated is this matter of muscular action. There is a natural 
tendency on the part of the infant to contract certain of the 
muscles of thfe body in a primitive gross combination. Thus, 


the infant can close the hand on any small object like a 
pencil which is laid across the palm. The fingers all enter 
into this act, and the muscular system of the hand and arm 
cooperate in a single performance. This primitive act is 
very like that exhibited by the animals lower in the scale 
than man. In the course of later life the child will have to 
acquire by practice the ability to move his individual fingers 
without including the others. Thus, if he learns to play on 
the piano, he must not move all the fingers together. In 
such a case he must learn to differentiate the fingers from 
each other. 

Conversely, there arises even in infant life the necessity 
of developing a careful cooperation between the different 
parts of the body. The two hands must work together in 
grasping an object. The head and eyes must turn toward 
an object which the hand is to grasp. Later in life the 
fingers which have become skilled in striking the piano 
keys separately must cooperate in striking the chord. 

In these examples the body is seen to be a highly evolved 
system of reacting organs constantly developing, on the one 
hand, in the direction of finer and more delicately adjusted 
movements and, on the other hand, in the direction of 
more complex combinations of these differentiated forms 
of behavior. 

In terms of our description we may distinguish three 
stages of muscular activity, always recalling that there are 
corresponding stages in the development of processes in 
the nervous system. First, there are gross adjustments ; 
second, differentiated forms of movement ; and third, coor- 
dinated forms of action. The term " coordination " here 
introduced will recur frequently in later discussions. Its 
meaning will be clear from the foregoing discussions. A 
coordinated movement is one in which groups of differen- 
tiated muscles cooperate under the control of nerve centers, 
thus producing complex but completely unified acts. 


Inherited coordinations or instincts. There is one impor- 
tant fact of heredity which must be included in the pre- 
liminary discussion of bodily movement before we are in a 
position to understand fully the relation of behavior to con- 
sciousness. The higher animals come into the world with 
many coordinated forms of behavior fully provided for in 
the inherited structure of their nervous systems. For ex- 
ample, a human infant is able at the beginning of life to 
use the lips and tongue in the complex act of sucking and 
he is able also to swallow through the cooperation of the 
muscles of the throat. Such an inherited complex of coor- 
dinated acts is called an instinct. The nervous centers in 
control of the lips and tongue are evidently coupled by 
lines of connection which the long experience of the race 
has laid down, and the infant is equipped from the first 
not only with differentiated muscles and controlling centers 
but with a fully developed organization in his nervous system 
which results in the cooperation of the differentiated centers. 

Glands as active organs. To this discussion of the devel- 
opment of the muscles and their contraction should be added 
the comment that there is another group of active organs ; 
namely, the glands. These secrete under the stimulus of 
the nervous system, and their behavior can for purposes of 
our discussion be regarded as like that of the muscles. 

A constant tension of active organs as background of all 
behavior. In order to understand the relation of the be- 
havior of the muscles and glands to consciousness, one 
general fact which is very commonly overlooked must be 
kept clearly in view. The active organs of the body are 
at all times during life in a state of tension. There are 
constantly pouring out of the nervous system streams of 
motor excitations. These are distributed to different parts 
of the body in currents of varying intensity, but there 
is always a stream of motor 'impulses going to the active 


One reason why this fact is not clearly recognized is that 
we ordinarily think of the nervous system as in action only 
when some part of the body is actually moving. Thus, if 
the hand moves from near the body to a distant point in 
order to pick up some object, we realize that the muscles 
of the arm are contracting. But if the individual sits 
rigidly in his seat, resisting the impulse to reach for the 
object, we overlook the fact that his muscles are on the 
stretch, often to an extent involving much greater effort 
than would be required to grasp the object. 

Evidences without end could be adduced to show that 
the muscles are in constant action. The neck muscles 
are constantly in action holding up the head of a waking 
man. Let the neck muscles relax for a moment, as they 
do when the man begins to get drowsy, and gravity will 
pull the head forward, giving a striking exhibition of the 
work which the neck muscles are doing most of the time. 

Again, consider what happens at all times by way of brac- 
ing the body for movements. The trunk muscles tighten 
when the hand begins to reach out because the trunk must 
balance the new weight which is taken up in the hand. 

Not alone the trunk muscles but the whole inner mech- 
anism of the body is drawn into action even by the most 
trivial movement. The blood circulation accommodates it- 
self to every act. This means that the contraction of an 
arm muscle calls for more blood to the arm. The call 
affects the heartbeat and the contraction of the muscles 
in the arteries which control the pressure of the blood in 
all parts of the body. The adjustment of blood circulation 
affects respiration and digestion and the inner glandular 
action, until finally the whole body is involved in the effort 
to move the arm. 

Meaning of sensory impressions dependent upon inner 
conditions. We are now in a position to understand the facts 
which were taken up in the early paragraphs of this chapter. 


A sensory impression does not come into a nervous system 
that is in suspense waiting to be aroused to action. A sen- 
sory impression is not the first or primary step in a series 
of nervous processes. The sensory impression comes into 
an inner world full of action. The new impression may 
change the mode of action or it may be absorbed into the 
processes under way. Again, using another figure, we may 
say that the inner world is constantly weaving its material 
into a pattern. The new sensory impression is new raw 
material. It may be necessary to shut down the machinery 
and recast the pattern in order to deal with this new mate- 
rial. Ordinarily it is not necessary to shut down. Ordinarily 
the new raw material is perfectly familiar and with very little 
disturbance of the routine is absorbed into the existing pat- 
tern, and the machinery goes on as it was working. 

Other analogies could be drawn on to help in describing 
the situation ; the best are always those which arc closest to 
mental life itself. Thus a social group receives a newcomer. 
The arrival is not the beginning of the group's social activ- 
ity. The arrival may make no striking impression on the 
conversation. On the other hand, the new arrival may turn 
all currents of thought and social life into new channels. 
The new social situation in any case will be the result of 
what was, plus the modifying influence of what now is. 

Sensory processes and the equilibrium of action. So it is 
in the action of the nervous system. Before a particular 
sensory impression comes, the nervous system is in a state of 
general excitation. Continuous streams of incoming sensory 
impulses and streams of outgoing motor processes constitute 
a complex of nervous life. The character of this complex is 
determined primarily by those inner paths of combination 
which have been developed in the organism's history and 
in its past struggles with the world. Into this inner world 
with its stresses and strains comes a new sensory impulse. 
In the great majority of cases the new impulse does not 


work any radical effect. The central processes are under 
way and they go on as before, absorbing into their main 
current the little stream of new sensory energy. Every now 
and then the new impulse is so strong or it fits into the 
workings of the central nervous system with such a power 
to change the equilibrium of action that a radical change 
takes place. One is reading and hears his name called 
from the next room. The name arouses action because it is 
imperative in its command over one's action. The call need 
not be strong, but it is one of the keys to a vigorous form 
of behavior entirely opposed to reading. In such a case the 
action is abruptly changed in its direction of operation. 

Importance of sensations dependent on organization. Even 
when one of the abrupt and impressive changes in central 
nervous action comes, it is not the sensory impulse as such 
which explains the change. The ability of the individual to 
react is here the chief consideration. An impression can 
never be strong unless the organization of the individual is 
prepared to receive it. Indeed, as pointed out earlier in the 
chapter, the whole evolution of the animal world indicates 
that the sense organs themselves evolve in the direction 
dictated by the demands for action. 

Sensations unduly emphasized through introspection. The 
discussion of activity as taken up thus far in this chapter 
has made very few appeals to the reader's conscious analysis 
of his own Experiences. The reason is that the view of con- 
sciousness here presented is not the one suggested by intro- 
spection. Introspection tends to bring into overcmphatic 
relief new sensory impressions. It is not difficult to note 
what goes on in consciousness when a color is seen or a 
sound is heard, for the points in consciousness where a color 
or a sound becomes vivid are relatively easy to distinguish 
from the main current of mental life. Consciousness pauses 
for a moment and gives emphasis to the arrival of the new- 
comer. It is much more difficult to look at the main current 


of experience because a person is in the midst of the cur- 
rent, absorbed in its movement and thus without any con- 
trasts by means of which to make himself vividly aware of 
that which fills his whole mind. Just as the social group 
which was referred to a few paragraphs back is not aware 
of its own atmosphere and of its own appearance but is 
clearly conscious of the new member, so personal conscious- 
ness must adopt new scientific methods of recognizing its 
own characteristics. 

Attitudes. Perhaps the use of a special term will help in 
bringing out what is here being emphasized. There is in 
every mental act an aspect which comes from the individual's 
reactions on his impressions. We may call this aspect of 
experience an attitude. Thus there are attitudes of liking 
and disliking. If the attitude is vivid, one may readily ana- 
lyze it out of the complex and say, " I like the color or the 
sound or the taste," or " I dislike the impression." If the 
attitude is not so vivid or so distinctive in character, it may 
be more difficult to separate it for purpose of study from 
the impression. A color may receive the attention of an 
observer, thus arousing a very definite and positive attitude 
called attention, but it is difficult to describe what one 
means by the word "attention." It is also difficult to dis- 
entangle attention from the color experience itself. Yet a 
moment's scientific consideration of the matter will make 
it quite evident that the conditions of attention are to be 
found in the individual's organization and active processes. 
No sensory impression carries in itself the qualities which 
command attention. Attention is a contribution of the inner 
world ; it is an attitude of the individual. 

Attitudes not related to sensations but to behavior. Our 
attitudes are as manifold as our modes of response to im- 
pressions and ideas. In the next chapter we shall select for 
treatment some of the chief attitudes of ordinary life. In 
the meantime', it is the purpose of this chapter to reiterate 



the fact that all attitudes are phases of behavior. The psy- 
chology of the individual must study modes of behavior 
quite as much as sensations. Indeed, if one is to be empha- 
sized more than the other, it is the business of science to 
bring out the significance of behavior, since this is likely to 
be overlooked by the superficial observer. 


Relation of sensation to reaction. It may be well to summarize 
the conclusions reached up to this point by means of a diagram. 


FIG. 44. Diagram showing relation of sensory impressions to reactions 

Let the rectangle at the left of Fig. 44 represent some object 
in the physical world a book or a piece of machinery. The ob- 
ject has many physical characteristics which are represented by the 
subdivisions i to 9. Some of these impress a human being ; others 
do not. For example, the machine may send out waves of electric 
energy for which we have no organ of sense ; the book may send 
out ultraviolet rays of light which lie beyond the range of vision. 
Subdivision 7 represents the power of emitting electric energy ; 
subdivision 8, the power of giving out ultraviolet rays. When 
energy from 7 and 8 reaches the surface of the human body there 
is no organ for the reception of the stimulation. Subdivision i, on 


the other hand, represents the power to reflect red light, and 
subdivision 2 represents solidity or resistance to touch. These do 
impress the human body if they strike the right points, as indicated 
by the dotted lines continuing lines i a and 2. Line i b represents 
a ray of light which does not strike the eye, but strikes some part 
of the skin and produces no effect. 

Let us follow the dotted lines which represent currents of sen- 
sory excitation entering the central nervous system from the eye 
and finger. It is not usual for the central nervous system to receive 
only two sensory impressions at any given moment, but for the 
sake of simplicity the others are omitted. 

As soon as these sensory processes enter the central nervous 
system they begin to flow toward the muscles which constitute the 
second surface of the body represented by the right-hand boundary 
of the rectangle standing for the individual. In the muscular sys- 
tem there are certain contractions /,,/, r, j, /, , and z>, which 
are the results of motor impulses flowing out from the nervous 

In the central nervous system the two incoming currents are 
brought together by the organized paths in this system. They then 
pass through the motor centers and are distributed in such a way 
as to reenforce s ; that is, one of the muscular tensions which was 
present from the first. 

We commonly say that the sensory impressions caused the 
reaction s. What really happened is that certain attributes of the 
object aroused the sensory impulses which in turn were fused by 
the individual's inner nervous organization in such a way that the 
reaction s of which the individual was all along capable was brought 
into emphatic play. 

Consciousness does not reflect merely the entrance of sensory 
impressions into the nervous system ; if it did, vision and touch 
from the same object would remain as unrelated facts in expe- 
rience. Consciousness includes the incoming impressions, but em- 
phasizes the fact that they are combined on the way to a common 
center of motor discharge. Consciousness is related to the central 
organization and thus to the reactions of the individual quite as 
much as to the incoming sensory impressions. 

We find ourselves, accordingly, in harmony with the conclusion 
to which our general study of the nervous system led us. We 


found, it will be remembered, that the indirect centers of the cere- 
brum that is, the organizing areas of the brain are the parts of 
greatest importance to the student of conscious life. We now see 
that this means that the fusion of sensory impressions on the way 
to their discharge as motor processes is the physical fact most 
closely related to consciousness. Consciousness does not depend 
primarily on the character of sensory impressions or of muscular 
contractions, but is determined largely by the organizing processes 
which follow the reception of sense impressions and their discharge 
into motor channels. 


Reactions toward objects and reactions away from objects. 

If we consider the simplest forms of animal behavior, we 
find that they divide into two classes ; there are, on the one 
side, activities in which the animal seeks those ends which 
gratify, such as food, warmth, and contact with its own 
kind ; and there are, on the other side, activities in which 
the animal seeks to escape from harm. The simplest 
animal forms show these two types of behavior, as has 
been pointed out in an earlier chapter (Fig. 2, and p. 16). 
The human infant shows the same fundamental forms of 

Pleasure and displeasure. There are in conscious life 
fundamental attitudes corresponding to these two types of 
behavior. We like what we seek, and our attitude toward 
impressions arousing this type of reaction is described by 
the common word " pleasure/' What we try to avoid 
arouses within us the opposite attitude, or one of dis- 
pleasure. In popular language the antithesis commonly ex- 
pressed is between pleasure and pain. Pain is, in reality, 
a very intense form of tactual sensation which comes from 
the injury of bodily tissues. Such sensations stir up the 
most violent efforts on the part of the organism to throw 
off the offending object ; hence the common failure to dis- 
tinguish between the sensory part of the experience and the 
attitude of displeasure. 

Pleasure and displeasure appear in a great variety of 
particular forms. Thus, when the body is taking in food, 



there is a series of activities which are among the most 
gratifying that the individual can experience. The nervous 
system is prepared to respond positively to the stream of 
sensory stimulations which come to the organs of taste and 
smell from objects suited to the organism. The organism 
is coordinated in its internal behavior to receive the objects 
that gratify, and the nervous activity accompanying the 
whole process is of the most favorable type. Again, the 
comfort of sitting in a warm, bright room is different from 
that of taking food ; but here, as in taking food, all the 
body's reactions are harmonious and favorable, and in a 
general way the attitude of the individual is of the same 
quality as that which appears in the act of taking food. 

Displeasure exhibits in like manner different forms. The 
odor of some object may be disgusting because it throws 
the body into violent activities aimed at rejection. In the 
same general way, one tries to get away from a glaring 
light. In both cases the action is one of self-protection, 
and the mental attitude is one of displeasure. 

There are negative conditions as well as positive which 
produce the typical attitudes of pleasure and displeasure. 
Thus the organism which is deprived of food or of warmth 
will make strenuous efforts to correct the deficiency, and 
the attitude which accompanies these efforts may be of the 
most intense displeasure. In like manner the relief which 
comes with the escape from impending danger may give 
the highest satisfaction. 

Cultivated feelings. In general, it may be said that what- 
ever impression promotes the normal reaction of the organ- 
ism is accompanied by pleasure ; whatever defeats normal 
behavior or arouses protective recoil is unpleasant. 

The history of psychology is full of efforts to classify 
pleasures and displeasures and to show the exact relations 
of these phases of experience to sensations. The difficulty 
in reaching any final classification is that with the progress 


of individual development new types of pleasure and dis- 
pleasure arise just in the degree in which one learns to seek 
or reject objects. Each human being starts with an instinc- 
tive tendency to seek certain ends and reject others. To 
these fundamental likes and dislikes he adds others con- 
nected with his mature experience. Thus each of us sets 
up certain property rights. One likes to have at hand, sub- 
ject to his instant command, certain conveniences. If one 
cannot find his pen or his tennis racket, he is sometimes 
thrown into a state of distress hardly less violent than that 
exhibited by the infant who cannot find food. The tastes for 
pens and tennis rackets are acquired by the use of these 
instruments, they are in no sense of the word instinctive ; 
but once the habits of use are organized they demand the 
opportunity for expression, and satisfaction or its opposite 
will attach to their presence or absence. 

Fear as a typical emotion. One of the significant exam- 
ples of a strong negative attitude appears in the experience 
which we call fear. We sometimes speak of the instinct of 
fear. There is, indeed, in every animal a strong tendency 
to run away from everything that is strange or large or 
overstimulating. So delicately is the nervous system poised 
to protect the individual that when a strange or violent 
stimulation comes to the organs of sense there follows an 
overstimulation of all the active organs. This overstimula- 
tion is accompanied by an inner state of agitation. The 
inner agitation confuses all thought and is a source of 
displeasure just because the inner chaos is ineffective and 
incapable of arousing any coordinated forms of expression. 
The frightened man is proverbially not intelligent. The fact 
is that the frightened man is internally in a commotion, and 
his mind is blurred because he cannot cope with the situa- 
tion. His motor processes are stalled or incoordinated, and 
his attitude is disagreeable and increasingly so the longer 
his inability to' deal with the situation continues. 


Fear is a form of displeasure, but unique as contrasted 
with the displeasure of rejecting an unacceptable taste or 
color. Yet so general in character is fear that it may attach 
to any violent form of excitement. Fear, which has been 
described as the most primitive form of human displeasure, 
does not disappear with modern life, but tends, rather, to 
become more general and more intense. To be sure, it 
attaches to new objects as man overcomes his first enemies, 
but it is one of the most common attitudes of life. Primi- 
tive inan was afraid of an eclipse ; modern man is not. 
Modern man is, however, thrown into a panic by an earth- 
quake because it runs counter to all his established forms 
of behavior to have the solid earth under his feet begin to 
rock. The earth has been the base of all behavior, and 
one is at a loss to control behavior when this base of action 
changes. Not only so, but modern life contains new terrors 
which were not known in earlier stages of civilization. The 
embarrassment of appearing in public is one of the new 
inventions of civilization. That there is much superfluous 
excitement in this case is realized by everyone whose knees 
have trembled and whose pulse has gone to one hundred 
and thirty. The mental distress of the situation comes 
from the fact that these forms of reaction are ineffective, 
indeed are quite absurdly in the wrong direction. 

How to change the attitude of fear. The common advice 
given to children to go directly and investigate any object 
of which they are afraid is in general good. The going 
and the handling of an object give the individual a form of 
reaction which is coordinated and normal as a substitute for 
the agitation and for the ineffective inner agitation. 

Fear an emotion of complex beings. Kipling has made a 
tale out of the evolution of fear. The stupid, slow-going 
bullocks in a night stampede in the camp tell how they 
fight and criticize the elephant as a coward. The bullocks 
tell how they draw the guns. 


" Then we tug the big gun all together Hey a Hullah ! 
Heeyah ! Ilullah ! We do not climb like cats nor run like calves. 
We go across the level plain, twenty yoke of us, till we are un- 
yoked again, and we graze while the big guns talk across the plain 
to some town with mud walls, and pieces of the wall fall out, and 
the dust goes up as though many cattle were coming home." 

" Oh I And you choose that time for grazing do you ? " said the 
young mule. 

" That time or any other. Eating is always good. We eat till 
we are yoked up again and tug the gun back to where Two Tails 
is waiting for it. Sometimes there are big guns in the city that 
speak back, and some of us are killed, and then there is all the 
more grazing for those that are left. This is Fate nothing but 
Fate. None the less, Two Tails is a great coward. That is the 
proper way to fight. We are brothers from Hapur. Our father 
was a sacred bull of Shiva. We have spoken." . . . 

Whereupon the elephant who has heard himself accused 
of being a coward replies as follows : 

" Well," said Two Tails, rubbing one hind leg against the other, 
exactly like a little boy saying a piece, " I don't quite know whether 
you 'd understand." 

" We don't, but we have to pull the guns," said the bullocks. 

" I know it, and I know you are a good deal braver than you 
think you are. But it's different with me. My battery captain 
called me a Pachydermatous Anachronism the other day." 

"That's another way of fighting, I suppose ?" said Billy, who 
was recovering his spirits. 

" you don't know what that means, of course, but T do. It 
means betwixt and between, and that is just where I am. I can 
see inside my head what will happen when a shell bursts ; and you 
bullocks can't." 

" I can," said the troop-horse. " At least a little bit. I try not 
to think about it." 

" I can sec more than you, and I do think about it. I know 
there 's a great deal of me to take care of, and I know that nobody 
knows how to cure me when I'm sick. All they can do is to stop 
my driver's pay till I get well, and I can't trust my driver." 


Two Tails stamped his foot till the iron ring on it jingled. 
" Oh, I'm not talking to you. You can't see inside your heads." 

" No. We see out of our four eyes," said the bullocks. " We 
see straight in front of us." 

" If I could do that and nothing else you would n't be needed 
to pull the big guns at all. If I was like my captain he can see 
things inside his head before the firing begins, and he shakes all 
over, but he knows too much to run away if I was like him I 
could pull the guns. But if I were as wise as all that I should never 
be here. I should be a king in the forest, as I used to be, sleeping 
half the day and bathing when I liked. I have n't had a good bath 
for a month." 1 

Fear and pathology. The physicians who deal with mental 
pathology report fear as the most common form of modern 
mental breakdown. The fears of our present-day lives are 
not the fears of the forest, but they are subtle and disorgan- 
izing. They cannot be classified merely as unpleasurable 
agitations ; they arise from violent and disorganizing forms 
of disrupted nervous activity. 

Parental love and altruism. Parental love for offspring 
has been described as an instinct. Here again we have to do 
with a complex attitude which can be understood only when 
one studies the forms of behavior which the parent culti- 
vates. Nature has so organized the higher animals that they 
protect their young. Gradually the compass of these protec- 
tive activities widens until a mother may be wholly absorbed 
in the care of her offspring. The evolution of many of the 
complex forms of social life is directly traceable to the 
efforts of parents to care for their young. Fiske, in a very 
interesting essay on the evolution of altruism, has shown 
how the care of the child has brought into the world a 
mental attitude wholly beyond animal instinct. Among primi- 
tive animals behavior was at first aimed at self-preservation, 
With the growth of parental solicitude has come a form of 

1 Rudyard Kipling, The Jungle Book, pp. 284, 287-289. The Century 
Company, 1914. 


behavior which is at times so strong that a mother will 
sacrifice herself and with supreme gratification undergo all 
kinds of hardships in doing for her child that which will 
protect him and promote his welfare. This in turn, as Fiske 
points out, leads to other altruistic acts and attitudes em- 
bracing companions and acquaintances. Cultivated modes 
of behavior may, as in this case, create mental values which 
are entirely unintelligible if we think only of individual 
self -protection. 

Anger. Anger is a mental attitude which accompanies an 
effort to throw off restraint. There may be blind rage in 
which the angry man beats aimlessly at everything which 
is within reach, or there may be the subtle studied anger 
which step by step proceeds to the final attack. Watson has 
called attention in his experiments with infants to the fact 
that a new-born infant will be thrown into a rage if its move- 
ments are restricted. Hold an infant's head perfectly still 
and anger will appear. 

Other emotions. The list of attitudes could be indefinitely 
amplified. Jealousy, shame, bashfulness, surprise, awe, rever- 
ence are all names of special attitudes which grow out of the 
efforts of the individual to deal in some active way with the 
world about him. They all reduce in the last broad analysis 
to pleasurable and unpleasurable experiences, but this gen- 
eral classification obliterates the distinctions which can be 
productively retained if, instead of merely trying to classify 
attitudes, one develops the formula of explanation which in- 
cludes all the rich variety of human reactions to a complex 

Emotions as fundamental forms of experience. The fore- 
going paragraphs will be recognized by every reader as deal- 
ing with that aspect of experience which has always been 
referred to under the terms " feeling " and " emotion." The 
importance of the feelings must not be underestimated by 
the student of human life. Sensory impressions are of 


significance only as they arouse attitudes. It is the attitude 
which reveals the individual ; and the attitude in turn is 
the result of organized modes of response. The paths in 
the nervous system along which sensory impressions travel 
to their motor discharge, the central agitations which arise 
in the nervous system as the sensory impressions are com- 
bined and recombined, condition experience in a way that 
cannot be overlooked by one who is interested in human 
nature. Human nature is what it is, not because of the 
impressions which come to the eye and ear, but because of 
the responses which are worked out through the central 
nervous system. 

Higher forms of experience as related to behavior. Thus 
far we have been showing in a general way that attitudes are 
related to reactions. The full significance of reactions for 
individual mental life will become increasingly apparent as 
the subsequent discussions canvass the different types of 
organized behavior of human beings. We shall discover that 
there are lower forms of behavior and lower types of mental 
attitude, and that the development of higher forms of expe- 
rience involves the development of higher and more complex 
forms of reaction. Indeed, the rest of our study will be a 
study of human reactions and accompanying experiences. 
The remainder of this chapter will be devoted to a study of 
some of the more primitive and more fundamental attitudes. 

Feelings of organic type. Many of the most primitive 
adjustments of the motor organs of the body are internal 
adjustments and have to do with the well-being of the body 
itself. Accompanying these there is at all times a background 
of feeling which colors all experience. There is the buoyant 
feeling which one enjoys when he begins life on a bright, 
clear day and the feeling of utter depression of a foggy day. 
The reasons for such feelings can be understood from such 
experiments as the following. The muscles of a waking 
person are always under tension. Let the tension be tested 


under conditions of varying stimulation. The individual can 
be asked to show his muscular strength by means of a 
dynamometer or simple apparatus for measuring the strength 
of the grip. If such a test is made in a dark, silent room, 
and a second test with the same person is subsequently made 
in a room which is well lighted and full of sound, it will be 
found that more work can be done in the latter case than 
in the former. The additional light and sound have raised 
the nervous and muscular tone to a higher level, so that 
when the movement is undertaken, the motor impulses to 
the muscles have the advantage of the higher initial tension. 
It need hardly be pointed out that the conscious experience 
of the reactor is different in the two cases described. 

Flexor and extensor movements related to characteristic 
attitudes. A second experiment is as follows : Let a person 
be trained to make an outward swing of the arm with his 
eyes closed. If a number of measurements are made, it is 
possible to determine with great accuracy the range of error 
of these movements. If the movements are 'made when the 
senses are in a quiet condition without special stimulation, 
they will not be of exactly the same length in successive 
trials, but they will not differ widely from each other. After 
these preliminary tests, let the reactor be given a strong 
bitter or sweet taste sensation. The result will be that the 
arm, in common with the other muscular organs of the body, 
will take on a different tension. The tension in the case of 
a sweet stimulus will tend to favor outward expansive move- 
ments ; the tension in the case of a bitter stimulus will tend 
to favor inward contracting movements. The result will be 
increased movements in these directions, even when the 
person tries to move as before. In short, bitter tastes and 
sweet tastes result in inner muscular tensions. 

Changes in circulatory movements as parallels of con- 
scious changes. One of the systems of muscles which is 
most noticeably affected by any change in stimulation is the 


system in control of the circulatory activities. If a recording 
apparatus is so adjusted as to give a record of the rate and 
intensity of the heartbeat, it will be found that there is a 
constant rise and fall in the rate and intensity of circulatory 
activity. The rise and fall can be shown in striking degree 
by using in the course of the experiment some marked 
stimulus, but even when no special stimulus is applied to 
the organs of sense, there is a continuous flux and change 
in the circulatory activities. Here, again, it is unnecessary 
to point out that consciousness is constantly changing, and 
that it changes most noticeably with the application of an 
external stimulus. Indeed, so close is the relation between 
activity and sensation in this latter case that it may safely 
be said that there is never a change in sensory excitation 
without a parallel change in circulatory activity. 

Disappointment as negative emotion. Another case of this 
internal type of reaction is to be found in the fact that the 
body is from time to time thrown back on itself. For ex- 
ample, one starts to go about some ordinary task and finds 
that the energy he had mustered up for the work cannot 
be used because he cannot find the tools for his work. The 
energy which was to be expended in doing the work is 
thrown back into the body, and the inner agitation is accom- 
panied by what we call in ordinary life disappointment. 
Here the nervous agitation is in the nature of a disagree- 
able stopping of movements which were originally directed 
outward but have suddenly been thrown inward. 

External attitudes. There are many forms of reaction 
with an outward turn which are less emotional in character 
because the content of experience is less personal. We use 
in such cases terms like " satisfaction " or " interest." The 
man who makes a good stroke in golf enjoys it and gets 
satisfaction out of it, but he does not have so intense a per- 
sonal experience as he has when he makes a bad stroke. 
The successful performance issues in a series of impressions 


and ideas rich in content ; the unsuccessful act arouses vio- 
lent internal circulatory reactions and unpleasant tensions of 
all the muscles of the body. 

Attention as an attitude. There is one very general fact 
with regard to reactions to external objects. The individual 
either turns toward an object, looking toward it, reaching 
out for it, and bracing himself to deal with it, or else the 
individual turns away from an impression, neglecting it or 
actually rejecting it. The attitude side of these various forms 
of response is described by a general term, the term "at- 
tention." One attends to an object or is interested in it, or 
in the other case he neglects it or exhibits a lack of interest 
or concentration on it. 

Experiment to demonstrate tension. Attention is the atti- 
tude of reacting to an impression. The physical symptoms 
of attention are well known ; there is the strained muscle, 
the fixed gaze, the leaning forward to catch the new im- 
pression which will in turn arouse more action. Much of 
the reaction exhibited in a state of attention is for the pur- 
pose of focusing the organs of sense on the source of the 
sensations. The infant is constantly trying to get into contact 
with everything for the purpose of getting more impressions. 

All through life there is a tendency to move in the direc- 
tion of an object which is in the center of attention. This 
is shown experimentally as follows : Let the person to be 
tested rest his hand on some recording apparatus which 
moves with very little friction. A board suspended by a 
long string and carrying a tracer at one end is a very good 
apparatus with which to make this experiment. Now let the 
subject close his eyes and think intently of his hand. The 
recording point will make short excursions back and forth, 
for there is no such condition as one of absolute rest of the 
hand muscles, and under the conditions arranged very slight 
movements are sufficient to produce a record. After noting 
the range and kind of movement which will be made when 


one thinks as steadily as he can of the hand, let the reactor 
think intently of some object at his right or left. Let him 
make an imaginary journey or draw in imagination some 
simple geometrical figure. The result will be that the move- 
ments of the recorder will be radically changed. There will 
often be a tendency for the 
new movement to take on 
a form directly related to 
the new subject of thought, 
but irj any case there will 
be a change from the type 
of movement which appears 
when attention is concen- 
trated on the hand, even if 
the form of the new move- 
ment is not directly trace- 
able to the new experience. 
Fig. 45 shows the records 
of involuntary hand move- 
ments of the type described. 
Various forms of atten- 

,01. FIG. 45. Involuntary hand iriovements 

tion. Such an experiment made 45 by the right y an d left hands of 

an observer who is thinking of a build- 
ing situated in front of him 

The hands begin at the two points A, A; 
the building lies in the direction of the 
movement which is here represented by 
the downward extension of the two lines. 
(After Jastrow) 

reveals the reason for the 
use of words like " atten- 
tion," " concentration, "and 
" interest " as partial syno- 
nyms. The focusing of ac- 
tivity on an object arouses 
an emotional attitude ; hence we are justified in treating 
attention and feeling as closely related. 

The explanation of attention will perhaps be understood 
most readily through consideration of those negative cases 
where the individual neglects the objects about him, as 
when we do not count the number of windows in a room. 
Here the impression goes into the nervous system, but 


is not made a center of any direct reaction. The impres- 
sion is lost in the mass of reactions ; it is not individual- 
ized. We say that it does not receive attention or arouse 

Sympathy with fellow beings. Such general comments 
on attention lead to the treatment of special cases. When- 
ever we see a fellow being trying to do something, we tend 
to share in the activity. The man who is lifting a weight 
arouses all who see him to like effort. The singer who is 
taking a high note will be followed by his audience with 
sympathetic muscular efforts. Attention in these cases 

issues in svmpathetic 

Sympathy involved 
in all recognition of 
objects. Sympathy ex- 
tends far beyond one's 

FIG. 46. Uruesthetical balance fell W bein S S - A11 

The two black spots are evidently not well sup- that W6 i 
ported by the fulcrum shown in the figure. There the term 

is a resets JJ^^E should be appreciation" belongs 

under the same head- 
ing. For example, let an observer look at an unsymmetrical 
drawing, such as that shown in Fig. 46. The long horizon- 
tal line with the black figures at its ends is not well sup- 
ported at the fulcrum given in the figure. The feeling of 
lack of balance in this figure is directly related to an active 
tendency on the part of the observer to offer his support 
to the line as it carries the larger figure, and this tendency 
to action which is inspired by the figures is accompanied by 
a distinctly disagreeable experience, because it is continually 
ineffective in producing its purpose. Examples of the feel- 
ing of pleasure which comes from harmonious complexes 
can be derived from the study of Greek architectural forms. 
The Greeks recognized the fact that a column with perfectly 


straight lines is not an aesthetic object. Such a column always 
seems to be weaker in the center than at the extremities, 
where there are larger masses of matter. There is therefore 
a feeling of unrest inspired in the observer lest the column 
should give way in the center, where the tension is great 
and the material relatively reduced. The Greeks, accord- 
ingly, made their columns larger in the middle than at the 
extremities, and the result was that the observer, seeing the 
reenforcement at the critical part of the column, has a feel- 
ing oi satisfaction rather than of unrest in looking at the 
lines. The term "sympathy" is not used here as a figure 
of speech. There is a real muscular tension involved in 
observing a column lifting a weight, and through this 
tension the observer enters into the situation as an active 

Illusion due to muscular tension. The presence of mus- 
cular tensions related to perception of weight can be demon- 
strated in certain special cases. If one prepares two blocks of 
exactly the same objective weight but of very different sizes, 
so that one is, for example, about a foot cube and the other 
three inches cube, the observer will find when he comes to 
lift these two blocks that the smaller block seems decidedly 
heavier than the larger one. The explanation of this fact 
is to be found in the muscular preparation of the observer 
when he first looks at the two blocks. The visual expe- 
rience from the small block leads him to prepare to do a 
small amount of work in lifting it, while the visual impres- 
sion of the larger block is recognized in terms of a totally 
different kind of muscular organization, which may be de- 
scribed by saying that the observer prepares to do more 
work in lifting the large block than he prepares to do in 
lifting the smaller one. When, with these differences of 
preparation, the observer lifts the two blocks, he finds that 
his preparation does not coincide with the demands forced 
upon him through his direct contact with the blocks. There 


is, therefore, a sharp disagreement between the original 
preparation based on vision and the subsequent experience 
dependent on touch. This disagreement expresses itself in 
the form of an illusion with regard to weight. This illusion 
is not due to sensations merely, but involves also prepa- 
ration for active response. There can be no doubt that 
whenever one looks at any ordinary object of manageable 
size, he prepares to lift it. The preparation consists in an 
incipient act, and this act is the physiological parallel of 
an important phase of the observer's mental process of 

Such muscular tensions common to many experiences. 
This illusion of weight and similar facts from practical life 
throw much light on the nature of the organization which 
was referred to when it was stated, in discussing the aesthetic 
attitude toward a column, that one sympathizes with the 
column in the work which it does in supporting the mate- 
rials placed upon it. There is a certain direct perceptual 
estimation of the fitness of the column to do its work. 
That estimation expresses itself immediately in the mus- 
cular tension which is aroused in the observer as an inte- 
gral part of the process of recognition. If the column is 
inadequate, the observer is led to a strained attitude of 
assisting it ; if the column is adequate to its task, there is 
an attitude of satisfied recognition. 

All consciousness a form of sympathetic attention. Thus 
we find that as human attitudes become more complex they 
are something more than feelings or emotions ; they include 
also sympathies and discriminations which become parts of 
higher intellectual recognitions. When one sympathizes with 
a column, it is not a mere vague, general response ; it is a 
discriminating response, bringing one into personal relations 
to the outer world. In all the higher stages of mental 
development 'one knows objects through one's sympathies 
with them. 


The discussion of attitudes leads us thus to broad con- 
clusions about the nature of consciousness. Consciousness 
is a function through which the individual attempts to put 
himself in harmony with the outer world. He translates 
the world into terms of his own responses and thus makes 
the objects outside of himself a part of his own inner life. 
After he has thus taken the outer world into his mental 
life, a new possibility arises that of carrying back into 
the external world some of the rearrangements which are 
first worked out in the purely subjective sphere. The indi- 
vidual, by first fitting himself to the outer world, learns how 
to mold the outer world to meet his inner needs and desires. 

Attitudes as related to higher processes of recognition. 
Psychology must study, then, those attitudes of feeling and 
sympathy by which the inner world absorbs impressions and 
makes them into personal experiences. It must then take 
up the higher processes through which inner experience 
is made effective in controlling the world from which 
impressions first came. 



Sensory experience always complex. The arrival of a 
sense impression in the central nervous system has been 
shown in earlier chapters to be only the first step in a 
series of processes in which this impression is combined 
with other sensory impressions and carried forward to a 
motor discharge. It is literally true that no sense impres- 
sion ever comes into the central nervous system alone. 
Even if we think of only a single sense organ, we realize 
that it sends to the central nervous system at every 
moment a series of impressions rather than a single sen- 
sation. Thus, when the eye is stimulated by a colored 
surface, it is not a single sensation which arrives in con- 
sciousness, but a whole mass of sensations. The different 
parts of the field would yield various shades and intensi- 
ties even if the receiving cells in the eye were all alike 
and all prepared to respond with absolute uniformity to 
the stimulus. But, as was shown in the chapter on sen- 
sation, various parts of the retina are different in their 
ability to receive impressions. The result is that a colored 
surface is the source of a most complex series of sensations. 

The matter is further complicated by the simultaneous 
arrival of impressions through different senses. Thus we 
not only see a surface, we also touch it and may smell 
it or hear it vibrate. At any given moment there are 
impressions leaching the senses not from a single object 
alone but from various objects. As we look at a colored 



surface we receive touch sensations from contact with our 
clothing and from the floor on which we stand ; we hear 
sounds from the next room and breathe in odors which 
have no relation to the colored surface. 

Sensation combinations or fusions. In the midst of all 
this world of sensations there must be selection and com- 
bination. The individual works out, in the interests of 
practical life, certain units of experience in which sensa- 
tions are fused with each other and distinguished from 
the rest of the world. For example, one sees an orange. 
What he really sees is a complex background in the midst 
of which there is a little patch of orange shade. He gets 
a mass of odors, but attaches a particular aroma to the 
particular patch of color. He is able, in the course of 
this attention to his experience, to recognize that the color 
and the aroma are nearer his right hand than his left. 
What he has done in thus fusing a group of sensations 
and locating the fused group on the right is designated 
in technical psychological language by the term " percep- 
tion/' One perceives objects ; that is, one recognizes cer- 
tain groups of sensations as belonging together and as 
different from the rest of the world. 

Space not a sensation, but a product of fusion. In the 
process of perceiving the world the individual develops 
certain types of conscious experience which must be dis- 
tinguished from sensations. Space is such a product of 
organized experience. Space results from the fact that 
sensations take on what we may call " togetherness." To- 
getherness is a product of fusion. The counterpart of 
togetherness is separateness. The perceived orange is dis- 
tinguished from other objects. The whole complex of 
togetherness and separateness ultimately gets arranged into 
a general map or system. In this system there ultimately 
comes to be a right and left, an up and down. The world 
is now recognized as arranged in order. 


Tactual space as a simple example of fusion. One of 

the earliest experimental studies in space perception dealt 
with the spatial arrangement of tactual experiences. In 
his effort to find some method of testing the sensitivity 
of the skin, Weber measured the distances which must 
lie between two stimulated points on the skin in different 
parts of the body before the points may be recognized as 
separate. He found that in much-used regions, such as 
the ends of the fingers, the lips, and the tongue, the distances 
which are necessary between points, in order that they may 
be distinguished, are very small, often less than a single 
millimeter; while on the upper arm or the middle of the 
back the points must be separated by three to six centi- 
meters in order to be recognized as two. Furthermore, as 
has been abundantly shown since the time of Weber, there 
is the greatest uncertainty in the estimation of distances 
and directions in the regions where discrimination of points 
is difficult. 

Subjective and objective space. On the basis of these 
facts we may emphasize the difference between external 
space and our recognition of space. Two millimeters of 
extension on the middle of the back are for the geometri- 
cian equivalent in all respects to the same distance on the 
finger. For the observer who perceives these two regions 
through th'e sense of touch, the recognition of the two dis- 
tances is not a geometrical fact, uniform for all parts of the 
body, but a complex of varying experiences. 

Perception and training. Experiments of the kind which 
Weber tried can be carried farther. Thus, it has been 
shown that after a little training regions of the skin where 
the discrimination was relatively difficult can be developed 
so as to permit of very much finer discrimination than 
that which was exhibited at first. In other words, without 
any radical change in the sensory conditions, practice will 
rapidly refine space perception. Again, if any region of the 


skin is stimulated by means of a continuous line rather than 
by two separate points, it will be found that the greater 
mass of sensations received from the line facilitates dis- 
crimination. A line can be recognized as having exten- 
sion when it is about one third as long as the distance 
between two points which are just discriminated as sepa- 
rate from each other. The difficulty of discriminating two 
points when they are presented alone is not due to the 
character of the sensations from the points, but rather to 
the difficulty of discriminating them without the aid of a 
more complete sensory series derived from the stimulation 
of points between. 

Development of spatial arrangements in the course of 
individual experience. In our search for an explanation 
of the facts of tactual perception of space, let us ask 
what is the course of individual development. Anyone 
who observes an infant recognizes that early in life there 
is the greatest uncertainty in locating stimulations on the 
skin. If the skin of an infant is vigorously stimulated 
either by some accident or by the efforts of someone who 
is interested in making an experimental investigation, it 
will be found that the infant moves its hands about in the 
most indefinite fashion, often failing entirely to reach the 
irritated spot. We can understand the infant's difficulty 
if we try to locate with precision some point which has 
been stimulated on the skin of the upper arm. The infant 
has sensation enough, just as we have when stimulated in 
an undeveloped region, but the sensation is not properly 
related to other sensations. It has no recognized relations 
which give it a definite place in a well-ordered sequence 
of tactual or visual qualities, because the well-ordered 
sequence has not yet been built up. An established series 
of relations of some definite kind is necessary before the 
sensation can enter into distinct spatially-ordered percepts. 
Until a definite series of space notions is developed, the 


sensation will enter only into vague fusions, and localiza- 
tion will be altogether incomplete. The change from vague 
to definite localization requires much experience and atten- 
tion. Indeed, it is a fact easily verified that no sensation 
becomes definite in its relations until the practical needs 
of life demand such definiteness. The reason why an 
adult discriminates points on the end of the finger and 
not those on his back is that in the course of life he 
has been obliged to use his finger sensations. Use has 
led to an arrangement of points, to the development of 
what may figuratively be called a map. This map is devel- 
oped by recognizing again and again the relation of a 
finger to the palm of the hand and of the palm of the 
hand to the elbow, and so on, until the various parts of 
the body are thought of as in a fixed relation. The map 
then takes on a kind of independence and remains in 
the mind as distinct from any particular sensations. The 
adult knows the parts of his body even when they are 
not actually stimulated at the moment. 

Vision and movement as aids to touch. This process of 
developing definiteness in tactual localization has undoubtedly 
been very greatly facilitated by the presence of vision. Even 
in adult life one can often find himself making his experience 
of a tactual stimulation more exact and complete by looking 
at the point irritated, thus relating the tactual sensation to 
visual sensations. The process of localization of tactual sen- 
sations is also very largely dependent on movement. It is an 
empirical fact that the perceptual arrangement of skin sensa- 
tions is most complete in the most mobile parts of the body. 
A number of careful experimental observers at one time ex- 
plored the whole surface of the skin and showed that in any 
given region that part which is most mobile is the part on 
which points are most easily discriminated. Thus the hand 
is the most highly developed part of the arm ; the foot is the 
most highly developed part of the leg. 


Tactual percepts of the blind. In some respects the tactual 
perception of blind persons is more highly developed than 
that of persons who have vision. The blind are not supplied 
with better organs of touch, but they make more discriminat- 
ing use of such experiences as they receive through the skin. 
They also make more use of movements than do normal per- 
sons, as may be observed in the fact that they restlessly 
explore every object which comes within their reach. The 
limitations of the space perception of the blind appear when 
complex objects are presented for recognition. When the 
mass of sensory impressions is great, the discrimination and 
fusion of these sensations become very difficult. This fact is 
strikingly illustrated by the history of the raised letters used 
in books for the blind. The most natural way of producing 
such books, and the way which was followed at first, was to 
print in raised lines the same letter forms as were used for 
persons who read visually. For vision the complex lines of 
ordinary printed letters offer no difficulties, because vision is 
so highly organized that it discriminates easily the ordinary 
printed forms. No one realized that touch being so much 
coarser than vision would discriminate forms less easily. 
Such proved, however, to be the case. The letters for the 
blind have, accordingly, been simplified until in one of the 
best and most recent systems the letters are made up entirely 
of points. These points are easy to distinguish and, being 
placed near one another, are also easy to recognize in groups, 

Wundt on the tactual perception of the blind. The char- 
acter of tactual perception in the case of the blind is thus 
illustrated and discussed by Wundt : 

The way in which the blind alphabet is read shows clearly 
how the space ideas of the blind have developed. As a rule, the 
index fingers of both hands are used in blind reading. The right 
finger precedes and apprehends a group of points simultaneously 
(synthetic touch), the left finger follows somewhat more slowly 
and apprehends the single points successively (analytic touch). 


Both the synthetic and analytic impressions are united and referred 
to the same object. This method of procedure shows clearly that 
the spatial discrimination of tactual impressions is no more imme- 
diately given in this case than in the case where vision was present, 
but that in the case of the blind the movements by means of which 
the finger that is used in analytic touch passes from point to point 
play the same part as did the accompanying visual ideas in the 
normal cases with vision. 

Lotze's local signs. Another method of describing the tac- 
tual perception of space is that adopted by Lotze, one of the 
earliest of the writers on physiological psychology. Every 
point on the surface of the body gives rise, said Lotze, to a 
tactual sensation which in addition to its general quality and 
intensity as a tactual sensation has a peculiar and character- 
istic shading due to the structure of the skin at the particular 
point where the stimulus is applied. Thus, if the same pres- 
sure is applied to the lips and the forehead, the resulting sen- 
sations will, in spite of general likeness, be slightly different 
in the two cases, because there is soft muscular tissue under 
the skin of the lips and hard bony tissue under the skin of 
the forehead. These slight differences between tactual sen- 
sations which are due to locality lead the observer to arrange 
his tactual sensations in certain systems or series. The quali- 
tative shadings are thus transformed into spatial series. The 
qualitative differences come to signify position and are con- 
sequently designated as local signs. Their character as local 
signs is derived from the spatial system to which they are 
referred ; they are individually merely qualitative differences. 

Inner tactual factors. The factors which enter into tactual 
space percepts are probably derived in part from the inner 
organs, such as the semicircular canals, the joints, and the 
muscles. From the semicircular canals, as pointed out in 
an earlier chapter, there is a constant stream of excitations 
reaching the Central nervous system with every change in 
the position of the body. The limbs in their movements 


give rise to sensations in the joints and muscles. While the 
child is exploring the surface of his body and attaining the 
degree of ability to discriminate points which is shown by 
Weber's experiments, he is also learning through muscle 
sensations to recognize distances away from the surface of 
his body by reaching for things about him. He is learning 
through the sensations from his semicircular canals that 
there is a fundamental distinction between " right side up " 
and oblique or inverted positions. He is learning through 
joint sensations to recognize how many steps must be taken 
to cross certain stretches of space. 

Space not attached to any single sense. The striking 
fact is that ultimately all these different sensory factors are 
arranged into the same space form. There is not one tactual 
space, and another space for muscle sensations, and another 
for joint sensations. All are fused into a single system. 
The spatial order is a relational fact ; that is, it is a product 
of the fusion or putting together of sensations. Whenever 
sensations are fused into the spatial relation they take on a 
character different from that which can be assigned to them 
when they are considered alone. 

General conclusions regarding tactual space. From this 
survey of the facts of tactual space we have derived several 
important conclusions. Space is a complex. Space is not a 
sensation quality, but a relational form of experience. Tactual 
space is not explicable without reference to the general for- 
mula of organization which includes other sensations also. 

We are, accordingly, justified in postponing the general 
explanation of space perception until we have taken up the 
facts regarding the arrangement of auditory and visual sen- 
sations in the spatial form. 

Auditory recognition of location. Experiments on the 
localization of sounds may be made as follows : Let a sound 
be produced in the median plane, which passes vertically 
through the head from in front backward, midway between 


the two ears. If the sound is simple in quality, as, for ex- 
ample, a sharp click of some kind, and the observer's eyes 
are closed so as to eliminate vision and make him entirely 
dependent on hearing, the localization of the sound will in 
the majority of cases be erroneous. The sound will always 
be localized somewhere in the median plane, but its exact 
position in this plane cannot be recognized. If, on the other 
hand, the sound is moved slightly to the right or left of the 
median plane, it will be found that the observer can local- 
ize the sound with great accuracy. The explanation of the 
observer's ability to locate sounds coming from the side is 
simple and depends chiefly upon the fact that the observer 
receives from such a sound different intensities of sensation 
in the two ears. From all positions in the median plane the 
two groups of sensations received in the two ears have equal 
intensities, whereas the intensities of sounds received in the 
two ears from any position outside of the median plane are 

Influence of movements in auditory experience of position. 
Undoubtedly here, as in the case of tactual space, the facts 
of movement are of great significance in organizing sensory 
experience. If a sound on one side of the head is more 
intense than the sound on the other, there will be a strong 
tendency to readjust the head in such a way that the stronger 
sound shall be made even more intense and the weaker 
group of sensations shall be made still fainter by the move- 
ment of the head. If a sound is in the median plane and 
there is difficulty in getting at its precise localization, there 
is frequently a noticeable effort on the part of the observer 
to bring the head into such a position that a more satisfac- 
tory determination of position shall be possible through a 
modification of the intensities of the sensations from the two 
ears. Often auditory perception issues in a movement which 
tends to faring the eyes toward the source of the sound. 
The same tendency which was noted in the discussion of 


tactual sensations to fuse various kinds of sensations into a 
single spatial system is obvious in this effort to supplement 
hearing by vision. 

Qualitative differences and localization. The explanation 
which has been presented can be made more elaborate by 
giving attention to qualitative differences as well as to differ- 
ences in intensity in the two groups of sensations received 
by the two ears. There can be no doubt that the external 
pinna of the ear modifies somewhat the character of the 
sound as it enters the auditory canals. If a complex sound 
strikes -the pinna from in front, its quality will be different 
from that which would result if the same sound is carried 
into the ear from behind. As a result of these qualitative 
modifications produced by the external ear, we are able to 
localize sounds even in the median plane, provided they 
are of complex quality. The human voice, for example, in 
the median plane of the head, can usually be recognized 
with great precision as coming from a point in front or 
behind. This is due to the fact that the voice is complex 
in quality. 

Distance of sounds recognized only indirectly. The dis- 
cussion of the recognition of the direction from which 
sounds come may be supplemented by reference to the fact 
that the recognition of the distance of sounds also involves 
a large body of organized experiences. If one hears the 
human voice sounding very faintly in his ears, his frequent 
experience with voices and their normal intensity when the 
speakers are near at hand will lead him to recognize that 
the person speaking is far away. Furthermore, the qualita- 
tive character of the sound as well as its intensity is modi- 
fied by the remoteness of its source, the elements of the 
sound being less distinct when it is transmitted from a 
great distance to the ear. The intensity and quality are, 
accordingly, both utilized in interpretations of distance so 
long as the sound is familiar. 


Unfamiliar sounds difficult to locate. In contrast to the 
relatively easy estimation of the distance of a familiar sound, 
it is extremely difficult to estimate the distance of the source 
of an unfamiliar sound. An experiment may be tried by 
producing an unfamiliar sound, such as that which results 
from snapping a card in the neighborhood of an observer's 
head. Until this sound has become familiar the errors in 
estimation of distance will be very noticeable. 

Visual space and optical illusions. If we turn from audi- 
tory space perception to visual experiences, we find a rich 
variety of examples which show how complex is the process 

FIG. 47. Muller-Lyer illusion 

The length of the horizontal line A is equal to the length of the horizontal line B. 
(For further discussion of the figwe see text) 

of arranging sensations in a spatial order. There are certain 
cases of incorrect perception of length and direction of 
figures in plane surfaces, constituting what are known as 
geometrical optical illusions. These are especially clear 
examples of complex perception. Take, for example, the 
illusion represented in Fig. 47. The two lines A and B are 
in reality equal to each other, but the observer will recog- 
nize at once that they seem to be of different lengths. The 
retinal image of each line is distinct and clear ; the apparent 
inequality cannot, therefore, be attributed to any confusion 
in the retinal processes ; it must be attributed to some kind 
of perceptual* complexity. The explanation of the source of 


this illusion has been the subject of much discussion, and 
it is probably true that no single statement will account for 
the apparent inequality of A and B. In a general way it 
may be said that one cannot look at A and B without 
including in his field of vision the oblique lines, and the 
oblique lines are such striking and unfamiliar additions to 
the horizontal lines that they are not neglected as they 
should be in perceiving the length of the horizontals. If, 
in addition to this general statement, we attempt to show 
in detail how the oblique lines affect the horizontals, there 
are a number of facts which may be noted. The oblique 
lines produce less of an effect upon some observers than 
upon others. This can be shown by making quantitative 
determinations of the intensity of the illusion. For this 
purpose one of the figures of the pair under discussion is 
made adjustable, and the observer sets it until it seems to 
him equal to the other figure. When the two seem equal 
they will be in reality different. The amount of difference 
can now be readily measured, and the results from various 
observers compared. Not only are the results of such meas- 
urements different for different observers, but the same indi- 
vidual will at various times give different results. 

Effects of practice. One especially significant case of in- 
dividual variation is that in which the observer deliberately 
sets about comparing the figures a great number of times 
for the purpose of becoming familiar with them. Three 
stages of change in interpretation show themselves in such 
a practice series. First, the observer takes a general view 
of the whole figure, as does the ordinary observer who 
looks casually at the illusion ; he gets in this case a strong 
illusion. Second, the observer tries to look at the long lines 
and neglect the obliques ; that is, he makes an effort to 
overcome the disturbing influence in a negative way. During 
this period of conscious neglect of the obliques the illusion 
grows somewhat weaker, but it does not disappear. Finally, 


in the third stage, the observer reaches the point where 
there is no need of an effort to neglect the obliques. In- 
terpretation may be said to be so completely worked out in 
this stage that the obliques and the long lines fall into their 
proper relations without interfering with one another. Each 
is included in the percept, but in its true significance. At 
this stage the illusion is entirely overcome. 

Percepts always complex. Such facts as these make it 
clear that a visual percept includes all the factors in the 
field of vision. If these factors are conflicting, they may 
result in grotesque misinterpretations. If, on the other 
hand, they are thoroughly assimilated into the percept, they 


Fiti. 48. Illusion of contrast 

The middle portion of the short horizontal line marked off by the verticals seems 
longer than the equal distance marked off in the long horizontal line 

take their appropriate relations and no longer disturb the 
total process of perception. 

Contrast. A great many other illustrations could be 
brought forward to show the relation of one part of the 
visual field to all other parts. Thus, one cannot look at a 
line on a large blackboard and fail to be influenced in his 
estimation of the length of the line by the large surround- 
ing space. Conversely, a line drawn on a small sheet of 
paper is always interpreted in terms of the paper as either 
relatively long or relatively short. Objects seem very differ- 
ent in size when seen outdoors and again in a small room. 
Fig. 48 illustrates this principle by showing a short central 
line as part of a long line in one case and as part of a 
short line in a second case, with the result that the central 
line seems to be of different lengths in the two cases. 


Common facts showing size to be a matter of relations. 
Other complications than those from the surrounding visual 
field also influence one's perception of size. The natural 
standards of size which depend upon familiarity and upon 
the relations of objects to one's own body are constantly 
influencing perception. Time and again descriptions have 
been given by observers of the fact that a road seems 
longer the first time one passes over it, when all the 
sights are unfamiliar ; and many have also referred to the 
fact Jhat places known in childhood always seem small when 
revisited in mature life. 

Physiological conditions of visual perception. The signifi- 
cance of all these facts for our understanding of visual space 
is not hard to find. Putting the matter in physiological 
terms, we may say that when series of visual stimulations 
from a given line or figure reach the visual center, they find 
there a larger series of excitations from other points on the 
retina and a series of organized modes of response derived 
from past experience. Each excitation takes its place in 
this complex. 

Psychological statement. Putting the same matter in psy- 
chological terms, we may say that every sensation becomes 
part of a fixed order. This order or spatial arrangement is 
something other than the sensations ; it is a product of 
perceptual fusion. 

Photographic records of percepted movements. A clearer 
understanding of the matter will be reached by considering 
the results of photographic investigations, in which the path 
of the eye movement in looking over certain illusory figures 
has been determined. In Fig. 49 there is presented one of 
the most striking of the illusions of direction. The long lines 
are in reality parallel with each other, but the obliques are 
far too distracting to permit the ordinary observer to recog- 
nize the true relations between the parallel lines. Fig. 50 
shows another illusion of direction. The oblique lines are 



parts of a single line, but seem to extend in slightly different 
directions because of the interrupting space between the 

FIG. 49. Zollner illusion 
The long lines are parallel with each other 

parallels. Fig. 5 1 shows the paths in which photographs indi- 
cate that the eye of an observer moved in attempting to look 
at the illusions discussed. In Fig. 5 1, A, the movement over 
the Zollner pattern is shown. It is evident from the move- 
ments indicated in the photographs that the sensation factors 
are not fully mastered so as to permit coordinated move- 
ments along the parallel lines. The result is that though 
these lines give perfectly clear retinal images, they do not 
stand in their true relations in experience. 
The photographs show that often there 
is sufficient fusion of the sensory factors 
to permit a single movement in follow- 
ing a line, and this single movement is 
in the general part of the field of vision 
in which the line lies, but it is only a 
gross general approximation to the line. 
This corresponds exactly to the fact that 
the experience of the figure consists of 
a gross general perception of the long 
line and its obliques. One observer, after these preliminary 
photographs of his eye movements in looking at the Zollner 

FIG. 50. Poggendorff 

A t B are parts of the same 
straight line 




6 B 



FIG. 51. These figures show the path followed by the eye of an observer 
in examining certain of the foregoing illusions 

In each of the figures the path of the eye movement is indicated by a supplemen- 
tary line. The numbers placed along these supplementary lines indicate the points 
at which a pause was made in the course of the eye movement. In Fig. 51, A, the 
observer was attempting to follow the long line of the illusion. It will be noticed 
that he departs from the long line, and at the extreme end of the movement, as at 
2 and 5, makes a short corrective movement by which he again fixates the long 
line. In Fig. 51, /?, the distracting influence of the vertical lines is obvious, as is also 
the difficulty of moving the eye across the open space in any such way as to reach 
the point of interconnection between the vertical and oblique lines. In Fig. 51, C, 
it will be noted that the eye movement is very free in that part of the figure which 
is overestimated, and much restricted whenever the eye approaches one of the 
acute angles. This is indicated by the frequent pause in 3, 4, 6, 7, 8, 9. In 8 it 
will be noted that the eye is deflected from the horizontal line by the oblique 


pattern, put himself through a series of quantitative tests 
with the figure. In this practice series he gradually over- 
came the distracting effects of the oblique lines, and the 
illusion disappeared. A second series of photographs taken 
after the practice series showed that his eye followed the 
long line with great precision. Photographs with other 
illusions show clearly the distracting effects of the additional 
lines as indicated in full in Fig. 46. 

Relation between size and distance. When we study the 
relation of size to distance from the observer, we find a 
series of complexities even greater than those which have 
appeared thus far. In order to demonstrate this experi- 
mentally an observer should first secure an after-image 
through the steady fixation of some bright object. The 
after-image covers a certain number of retinal elements and 
may be considered as giving, as long as it lasts, a constant 
group of sensations. When the observer is looking at the 
object this mass of sensations will be interpreted as having 
a certain definite size and distance. When the same mass 
of impressions comes from the after-image, it can easily be 
related to different distances, and with each change in ap- 
parent distance it will take on a different apparent size. 
The change in distance can easily be produced by looking 
at various surfaces which are at different distances. The 
after-image will seem in each case to be on the surface at 
which the observer is looking at the moment, whatever the 
distance of that surface. The after-image will seem smaller 
when the surface on which it is projected is nearer than the 
original object from which the image was derived, and larger 
when the surface is farther away. 

Definite optical relation between the distance and the size 
of an object and the size of the retinal image from this 
object. This series of observations makes it clear that the 
size of a retinal image does not determine the interpretation 
of the size of an object without reference to the additional 



fact of distance. A given retinal image, for the after-image 
on the retina remained the same throughout the series of 
observations, may be interpreted as a large object far away 
or as a small object near at hand. The optical principle 
which underlies this series of observations is illustrated in 
Fig. 52. In this figure the retinal image is represented by 
the inverted arrow AB, and the lines from the extremities 
of this image passing through the optical center of the lens 
determine the positions of various external objects, any one 
of which satisfies the image. It will be seen from this 

FIG. 52. The retinal image AB may be equally well related to any one of 
the objects ab, a'b', a"b" 

drawing that a succession of arrows outside of the eye, differ- 
ing in length from each other, may all cast the same retinal 
image. This general principle is doubtless familiar to every- 
one when stated in the following simple terms : A small 
object such as the finger held near the eye can shut out the 
image of a large remote object, such as a tree or a building. 
When, now, the after-image in the experiment is projected 
to distances near and far away, its significance and perceptual 
interpretation are immediately modified, even though the 
retinal sensations are uniform in volume and distribution on 
the sensory surface of the eye. 

Berkeley's statement of the problem of visual depth per- 
ception. These observations lead us to a problem which was 
so clearly stated by one of the early writers in the modern 


period of psychology that we may quote his statement in 
full. In a treatise published in 1709 Bishop Berkeley said: 

It is, I think, agreed by all that distance of itself, and immedi- 
ately, cannot be seen. For distance being a line directed endwise 
to the eye, it projects only one point on the fund of the eye 
which point remains invariably the same, whether the distance be 
longer or shorter. I also acknowledged that the estimate we 
make of the distance of objects considerably remote is rather an 
act of judgment grounded on experience than of sense. 

Berkeley goes forward in the remainder of the " Essay toward 
a New Theory of Vision " to account for this process, which 
he calls a process of judgment. He draws attention to the 
fact that whenever one looks at an object near at hand he 
rotates his two eyes toward the nose so that the points of 
view from which he observes the object are different in the 
two eyes. He asserts that the convergence of the two eyes, 
as their inward rotation is called, gives rise to certain experi- 
ences of movement, which are utilized as interpreting factors. 
Experiments on binocular vision. The researches of 
modern experimental psychology have confirmed, in general, 
Berkeley's explanation, though they emphasize more than 
he did the differences between the two sets of retinal im- 
pressions received in the two eyes. The fact that the two 
eyes contribute a complex of sensations through which we 
perceive distance has been abundantly confirmed. The 
reasoning involved is as follows : If distance is recognized 
as a result of a complex of sensations coming from the two 
eyes, then it should be possible to show that the recognition 
of depth is seriously interfered with by the withdrawal of 
any of the factors contributed by the two eyes. It is not 
possible to remove altogether the influence of both eyes, 
even when one is closed ; hence, vision can never be reduced 
to strictly mqjiocular vision, but the following simple experi- 
ment may be tried to show the dependence of the clear 


recognition of depth upon vision with two eyes. If an ob- 
server covers one eye and then attempts to bring his finger 
directly over some object which stands in front of the open 
eye, he will find that the ability to bring the finger directly 
over the object in question is very much less than his ability 
to do so under the ordinary conditions of binocular vision. 
A direct observation of the same general fact can be made 
if the observer will note carefully the difference in the ap- 
parent solidity and remoteness of objects when he observes 
them first with a single eye and immediately afterward with 
both eyes open. These observations show that the complete 
recognition of distance and depth involves all the sensory 
factors from the two eyes ; whenever there is any disturbance 
of the normal conditions the result appears in incomplete 
perception, for the relational or perceptual process does not 
in such cases have its normal complex of content with which 
to deal. 

Difference between the images in the two eyes. The con- 
tributions made to experience by the two eyes are different, 
as can be clearly seen if an observer will hold some solid 
object near the face and look at it, first with one eye open 
and then with the other. The difference between the two 
views in the two eyes can be briefly defined by saying that 
with the right eye one sees more of the right side of a solid 
object and less of the left side, while with the left eye one 
sees more of the left side of a solid object and less of the 
right side. These relations are made clear in Fig. 53. 
When the two retinal images from the solid object are 
received by an observer, they are immediately fused with 
each other into a single perceptual complex, as were the 
two groups of auditory sensations discussed in an earlier 
section of this chapter. 

Stereoscopic figures and appearance of solidity. There is 
an apparatus often used for purposes of amusement, in which 
the principle that the appearance of solidity depends upon 



disparity of the two retinal images is utilized to produce the 
appearance of solidity even when no solid object is present. 
The apparatus in question is the stereoscope. Photographs 
are taken or drawings are made, corresponding in form to 

the retinal images which 
would be obtained by two 
eyes if they were look- 
ing at a solid figure or 
series of figures at differ- 
ent depths. The two 
drawings or photographs 
are then projected by 
means of the stereoscope 
into the two eyes of an 
observer in such a way 
that the right retina is 
stimulated by the image 
appropriate to the right 
eye, and the left retina 
is stimulated by the fig- 
ure appropriate to the 
left eye. The observer, 
who thus receives the 
sensory impressions ap- 
propriate to solidity, will 
naturally fuse the two 
images and will see in 
space before him a solid 
object which, in reality, 
is not there, but which 
is adequately represented by the two flat drawings projected 
into his eyes. A great many experiments can be tried with 
the stereoscope which make clear the significance of the 
two retinal images for the recognition of solidity and depth. 
It can thus be shown that the fused resultant, that is, the 

B C 

FIG. 53. Showing binocular parallax 

The cube BDAC is held near the two eyes 
with the result that the right eye sees the 
surface DA and the right side of the cube, 
while the left eye sees the surface DA and 
the left side of the cube. If a plane is passed 
through the rays of light which enter the eye 
from the cube, as indicated by the dotted line 
in the figure, it will be seen that the retinal 
images of the two eyes contain each a distinct 
element. The eye on the left-hand side of the 
figure has a retinal image corresponding to 
BD, which is absent in the other eye. Further 
details will be obvious from the figure 


percept of a solid object, does not derive its characteristics 
from either one of the retinal impressions considered in 
itself, for each image so considered is deficient in solidity. 
The fusion is, in a very proper sense of the word, a compro- 
mise between the two different images, and there appears as 
a result of fusion at least one characteristic which neither 
figure had in itself; namely, the characteristic of clearly 
defined solidity. 

Retinal rivalry. When the binocular images are totally 
different, as in certain experiments which may be arranged 
with the stereoscope, the observer finds that it is impossible 
for him to fuse the two groups of impressions. Thus, if he 
looks with one eye at a series of horizontal lines, and with 
the other at a series of vertical lines, he will see the fields 
in succession. The group of sensations coming from one 
retina will first be recognized in clear consciousness and 
will then fade out and give place to the sensations derived 
from the second retina. There is thus an oscillation in 
experience which is vividly described by the term " retinal 
rivalry/' In retinal rivalry there is obviously a lack of fusion 
of the sensations. The artificial differences in binocular 
images here produced are so foreign to the experiences 
which present themselves in ordinary life that the observer 
is unable to fuse them into a single conscious process. If 
such strange combinations of sensations are to be in any 
way related, it must be in a temporal succession of mental 
activities rather than in a single spatial form. 

Factors other than those contributed by the two eyes. 
The recognition of depth through the fusion of two groups 
of retinal sensations is not the only form of visual recogni- 
tion of depth. Other factors of experience and other types 
of relation may enter into the complex. In every case, how- 
ever, the factors or relations which contribute to the inter- 
pretation of solidity are, like the differences in binocular 
vision just discussed, complexes which get their significance 


and value not because of their sensation qualities but by 
virtue of the relations into which the sensations are brought. 

Aerial perspective. The first facts to which reference may 
be made are the differences in colors and sharpness of out- 
line which appear when objects are seen through different 
thicknesses of atmosphere. Remote colors are always dull 
and darker in shade than colors near at hand, and the out- 
lines of remote objects are ill-defined. We are so trained 
in the interpretation of these general facts that in looking 
at a landscape we pay very little attention to color quality or 
to the lack of clearness in outline, but utilize these immedi- 
ately for purposes of depth perception; that is, the sensa- 
tions are not recognized as distinct facts in experience, but 
are allowed to serve their function, which is to indicate the 
position of the object from which they come. Let the ob- 
server carefully compare his experience of distant fields in 
the landscape with fields near at hand. He will find that 
the remoter greens are blue in cast, even though under 
ordinary circumstances his attention is not directed to these 
differences in color shades. The same truth is well illus- 
trated by the fact that persons who have been accustomed 
to living in a moist atmosphere always misinterpret distances 
when they go to regions where the air is clear and free from 
moisture. Great distances seen through clear air are under- 
estimated because of the small effect which the air produces 
in modifying the colors and outlines of objects. 

Geometrical perspective and familiarity. Another impor- 
tant means of recognizing depth is through the familiarity 
which we have acquired with certain common objects. If a 
given object is carried farther and farther away from the 
eye, it will cast upon the retina a smaller and smaller image. 
If a man first observed at a distance of ten feet moves to 
a distance of twenty feet, the size of the retinal image and, 
consequently, the mass of sensations derived from this man 
will decrease one half. We seldom interpret such changes 


in the size of a retinal image of a familiar object as changes 
in the size of the object itself ; thus, we never say that a 
receding man has dwarfed to half his original size. We 
have learned by long experience that most of the objects of 
our environment are permanent in size and that the changes 
in our sensations merely indicate changes in the position of 
these objects. In this way we build up an elaborate series 
of recognitions of differences in depth. How completely we 
depend upon this recognition of familiar objects for our 
interpretation of unfamiliar or undefined experiences will be 
recognized if it is remembered that the interpretation of the 
size and distance of objects in photographs is always uncer- 
tain unless some familiar figure, such as that of a human 
being, appears as a scale by which to gauge the sizes of the 
other objects. 

Shadows. Another factor which is sometimes significant 
in giving rise to the interpretation of depth is found in the 
shadows cast by objects. The apparent solidity of a bank of 
clouds in the sky cannot depend upon binocular differences, 
because the clouds are too remote. They are also quite un- 
familiar, and may be without color ; therefore the methods 
of interpretation which we have described up to this point 
are quite inadequate to explain their apparent solidity. The 
shadows which they cast upon each other are, however, so 
clear in their indication of differences of position with refer- 
ence to the sun that we immediately recognize a bank of 
shaded clouds as made up of parts differing in distance from 
us. The same principle of recognition of solidity is utilized 
in all flat drawings intended to represent solid objects. Such 
flat drawings can always be made to suggest solidity with 
vividness when they are shaded in a way corresponding to 
the objects themselves. 

Intervening objects. Finally, we make use of the fact that 
near objects very frequently cut off our vision of remote ob- 
jects. Thus, if a tree which can be seen in all of its parts 


cuts off a portion of a house or other object, we perceive 
the house not as divided by the tree but as standing behind 
it. Here again we interpret our sensations as indicating dif- 
ferences in position rather than differences in the objects 

Depth a matter of complex perception. One cannot re- 
view this series of facts with regard to the visual interpreta- 
tion of depth without being confirmed in his view that space 
perception is a process in which sensory factors are related 
to each other in the most complex manner. No retinal im- 
pression has its value for mental life fully determined until 
it is brought into relation with other sensations. 

Relation to movements. As in the case of tactual percepts, 
so here there is a close relation between visual space and 
movements. In the first place, movements of the eyes are 
intimately related in their development to visual recognition 
of space. When an infant attempts to turn his two eyes on 
the same point of fixation, his movements are frequently so 
slow and irregular that they have the appearance, especially 
in photographs, of cross-eyed movements. Even in adult 
life it is shown by rapid photographs that the two eyes often 
move to a point of fixation in such a way that while one eye 
moves rapidly, the other comes up in an irregular, relatively 
slow movement. The development of a coordinated move- 
ment is thus seen to be the product of effort and concentra- 
tion. That a coordinated movement has been developed at 
all shows how significant it is for the individual that he 
should acquire a unitary motor response to the complex of 
retinal sensations. The unity of response stands, indeed, in 
sharpest contrast to the complexity of the sensory factors. 
The organized ability to coordinate the two eyes depends on 
the development of a system in which each phase of experi- 
ence, without losing its individual reality, is taken up in the 
single unitary system. Space and the coordinated system 
of ocular movements are thus seen to be very intimately 


related. The complex of movements has a unity which re- 
sults from the union of all of the different phases of binocular 
movement into a single coordinated act. Space is also a 
system in which every point has a certain character of its 
own and at the same time has characteristics which attach 
to it as part of the general system. 

General movements as conditions of fusion of retinal sen- 
sations. In the second place, the relation of visual space 
perception to organized behavior becomes clearer when it 
is noticed that the unity of visual percepts is demanded not 
only in the coordinations of eye movements but also in the 
coordinations of all forms of behavior which are guided by 
vision. If one reaches out his hand to grasp an object, his 
sensory impressions of the object will be derived from two 
eyes, but the reaction to be effective must be to all the 
sensations at once. 

Space a system of relations developed through fusion. 
Our treatments of space perception in the sphere of touch, 
hearing, and vision bring us to a general conclusion that 
space is a closed system built up through the fusion of 
sensations and, further, that this system is closely related 
to bodily movements. 

Movement and mechanical laws. The evidence that 
there is a close relation between space and bodily move- 
ment appears in the fact that space as we perceive it ex- 
presses those mechanical laws which govern all bodily 
movements. Human central nervous organization and re- 
lated muscular movements are, from the very nature of 
mechanical law with which the movements must comply, 
capable of only a very definite system of developments. 
One cannot move his hand at the same time toward the left 
and the right. Left and right come to be, therefore, clearly 
distinguished directions in the organization of human re- 
sponses to sensations. One cannot move his hand back- 
ward and forward in the same movement. As a result, all 


sensations which are to be related to movements are ulti- 
mately assigned to places either in front or behind, never 
in both positions at the same time. The child begins life 
without a thorough organization of his movements and, 
correspondingly, without any definite spatial forms of per- 
ception. The two develop together as he actively adjusts 
himself to the world about him. Finally, as he becomes 
master of his movements he finds that his perceptual world 
also has taken on certain definite sequences of arrangement 
which are so stable and systematic and so harmonious with 
what he comes to know theoretically of mechanical law that 
he can study the spatial system as he finds it in his per- 
ceptual consciousness and relate this spatial form of percep- 
tion to his science of mechanics without the slightest fear 
of finding any incongruity in the two groups of facts. It 
should be noted here again that such a complete system of 
space is much more than a series of sensations. Sensation 
qualities are necessary as the factors with which the indi- 
vidual must deal ; they constitute the material or content of 
experience, but the spatial form of perception is a product 
of perceptual fusion. Every sensation is related to every 
other not because of its quality or intensity but because 
every sensation must, in the organization of impressions, 
take its place in a serial system before it can serve any defi- 
nite function in individual life or have any clearly marked 
place in consciousness. 

Perception of individual objects. There are many forms 
of perceptual fusion which supplement the fusions entering 
into the closed system of space. To the ordinary observer 
an object recognized through the two senses of taste and 
smell is so unitary in character that he does not realize that 
any fusion of discrete sensations has taken place. By a 
simple experiment one can easily show that the perception 
of any article of food involves a number of distinct sensa- 
tions. Let the observer taste of some familiar substance, 


such as coffee, and at the same time, by holding the nose, 
prevent the air from coming into contact with the olfactory 
organ, and coffee becomes a sweet liquid with little or no 
flavor ; even castor oil becomes an inoffensive thick oil 
under like conditions. Why is it that in ordinary expe- 
rience tastes and odors are united ? It is because, in spite 
of the separation of the gustatory and olfactory organs, there 
is a constant demand in life that tastes and odors shall be 
used together in guiding conduct. The whole inner organi- 
zation of the individual is such that these different sensory 
qualities have a joint significance for perception and for 
behavior. There is a distinction on the qualitative side 
between tastes on the one hand, and odors on the other, 
because the sensory organs for the two qualities are differ- 
ent ; but there is the most intimate perceptual fusion to 
serve as a guide to conduct. 

There are perceptual fusions in every sphere of sensa- 
tion quite as compact as those of taste and smell and as 
various in character as the objects in the world about us. 

Mere coexistence of sensations no explanation of unity 
in the percepts of objects. The physiological condition of 
this unity in the perception of single objects is not to be 
found in the sensory processes themselves, any more than 
was the physiological condition for the perception of space. 
The sensory processes derived from things are very differ- 
ent in type and in the points at which they are received 
into the central nervous system. The unity of perception 
is not to be accounted for by the fact that all the sensory 
excitations are in the brain together, for not all of the sen- 
sations that are in consciousness at the same time fuse into 
a single percept. When we recognize a single object we 
do so by distinguishing it from its surroundings as well as 
by fusing its various attributes into a single percept. Thus, 
one recognizes the book he is reading by distinguishing it 
from his hands and from the bookcase in the background. 


Range of fusion determined by practical considerations. 

Again, as in the treatment of the fusion which leads to 
space perception, we must appeal to the central coordina- 
tions which are worked out under the stress of practical 
demands. One fuses sensory factors into the percept of a 
thing because he can adjust himself to certain aspects of 
experience in a single act. Thus, one speaks of a book- 
case and its contents as a single object when he merely 
wishes to name over the articles of furniture in his room. 
He distinguishes the separate books as objects when he 
wishes to take them out and use them. The range of one's 
experience of a thing is thus seen to depend not on sen- 
sory processes but on the practical motives which lead to 
the synthesis of more or less comprehensive groups of 
these sensations into single phases of experience. 

Changes in percepts through repetition. The fusion of 
factors into single groups becomes easier after repetition. 
Thus the expert rifleman comes to recognize at once the 
movement of his game, the distance of the game from 
himself, and the wind which will influence his shot, factors 
which might have coexisted indefinitely without being fused. 
All this he has acquired as the result of repeated efforts to 
shape his conduct in accordance with the demands of his 
total environment. Indeed, such a case of acquired fusion of 
widely divergent sensory factors may very frequently involve 
in its earliest stages conscious effort to adapt action to whole 
groups of sensations. The unity is made more and more 
compact as repeated efforts are undertaken to recognize the 
factors together, so that ultimately the perceptual unity, which 
began in a conscious relating of factors, becomes a synthetic 
unity of the ordinary type ; thus, we learn to see pen and 
hand and paper together when we learn to write, until all 
the f actors ^ which enter into the act of writing and its con- 
scious control are unified, and the final consciousness seems 
very simple, although it is a complex of many factors. 


Parallel development of perception and habit. Discus- 
sions of perceptual fusion might be carried over directly into 
the discussion of habits so as to show that the development 
of organized perception and the development of organized 
activity always go hand in hand. The training of eye and 
hand in any technical art, of ear and vocal cords in singing 
or speaking, of ear and hand in playing a musical instru- 
ment, go together in practical experience. The expert in 
every line not only acts more skillfully but he sees or hears 
more skillfully and comprehensively. Perception is discrimi- 
native and complete just in so far as the factors of experi- 
ence are organized into wholes appropriate for individual 
reaction. Our present purposes, however, can be fully satis- 
fied without a complete study of habits. The perceptual 
fusion involved in the recognition of an object is one phase 
of organization ; habit is an expression of this organization 
and will be taken up in a separate, later chapter. 

Time as a general form of experience. Before leaving 
the subject of perception it is important that we consider 
briefly a form of arrangement which has often been re- 
garded as similar in character to the space form ; namely, 
time. Time, like space, involves a relation between several 
factors of experience. Like space, it is not a sensation 
quality. It is even more general in character than space, 
for it is not merely a form of perception ; it is also, and 
indeed chiefly, a form of the indirect, or memory, experi- 
ences. A percept is always in the time series, but it is 
always in that portion of the time series which we call 
"the present." It will, accordingly, be appropriate for us 
to discuss in this connection some of the attributes of " the 
present, 1 ' leaving the other phases of time consciousness to 
be taken up in connection with memory. 

Experimental determination of the scope of " the 
present." "The present " is not a single point of expert 
ence ; it is a group of experiences. Some experimental 


evidence as to the possible length of "the present" may 
be gained as follows : Tap rapidly on the table at inter- 
vals of half a second or less, producing a series of sounds, 
and find how many taps of this kind can be grouped into 
a single easily apprehended unity. The observer will have 
little difficulty in determining the limit of such a series if 
he will simply listen to the taps and refrain from counting. 
A short series of five or six taps will leave behind in 
consciousness a feeling of perfect definitencss and ease of 
apprehension. If such a series is exactly repeated, or if a 
second slightly different series is sounded, the observer 
will be in no doubt as to the likeness or unlikeness of 
the two series. If, on the other hand, a series of twenty 
or thirty taps is sounded, the observer will recognize that 
at a certain point in the series a state of confusion sets in. 
The series is no longer apprehended as a unity, but has 
a vaguely defined massiveness which seems to elude the 
mental grasp. 

Scope of tf the present " and its varying conditions. The 
ability of the observer to group together a series of experi- 
ences is radically modified when the series itself is changed. 
Thus, if every third tap is made stronger than the others, 
or if it is given a slightly different quality, as in a series 
of musical notes, the scope of the immediately recognized 
group will be much increased. If the taps come irregu- 
larly, either in point of interval or in point of intensity or 
quality, the scope of the unitary group will be decreased. 

Time relations in verse and related systems of experience. 
All these facts appear in such practical forms of time per- 
ception as those which are utilized in making up English 
verse. The recognition of the successive feet in poetry is 
facilitated by grouping the sounds into simple compact 
groups. The character of each group is determined by 
variations iA intensity, quality, and content in such a 
large number of ways as to satisfy the demand for novelty 


in experience, while at the same time retaining very fully 
the characteristics necessary for temporal uniformity in the 
successive groups of factors. 

Time arrangement as conditioned by the rhythmical 
changes in nervous processes. To find a precise physio- 
logical basis for the time grouping of experience will 
require the discovery of processes which are much more 
general than those which constitute the physiological basis 
for space perception and for general perceptual unity as 
exhibited in the recognition of objects. Indeed, we must 
go far enough, as indicated above, to recognize that the 
conditions of temporal discrimination are involved in indi- 
rect memory processes even more than in perception. 
Such a general characteristic is to be found in the fact 
that all nervous processes are constantly fluctuating in 
intensity because the inner nervous condition is never 
in equilibrium. The nervous condition is a living process, 
now rising to a higher intensity, now declining to a low 
intensity. This can be seen if an observer will pick out 
in the constellation Pleiades a faint star which is just 
visible, and watch it for a time. He will find that- it disap- 
pears and then reappears for an interval, only to disappear 
again. The rhythmical change is here so complete that 
it is perceived as a change in the object. A like fluctu- 
ation of intensity is present in all sensory impressions, 
even if the sensation is so strong that its decrease in 
intensity does not cause it to disappear entirely. 

Perception more than the flux of sensations. In addition 
to the fluctuations in experience which result from the con- 
ditions in the nervous system, there are changes which arise 
from the relation of the observer to the object. For example, 
as one makes his way down the street he sees some object 
for a moment and then loses sight of it until he comes 
once more to a point from which he can observe it. In all 
this flux of experience action must be based on a recognition 


of the permanency of objects which transcends present 
sensations. We project our fluctuating sensations into a 
series which provides for time changes which are not 
changes in the things themselves. Thus we find new evi- 
dence" that experience is organized out of sensations but 
goes far beyond sensory qualities and intensities in the 
attributes which it exhibits. Time is not a sensation ; it 
is a form in which sensations are held because the mind 
recognizes in objects a permanency which extends beyond 
present personal experience. 


Discussions of perception. The discussion of perception may 
be closed with a brief summary. Perception involves, first, a 
spatial order ; second, the compact fusion of sensations into 
percepts of separate objects in the world ; and third, the begin- 
ning of a temporal order. The spatial arrangement is intimately 
connected with movement, being the arrangement given to sen- 
sory factors under the mechanical demands for characteristically 
different reactions to different sensory factors in the total mass 
of experience. Fusion of sensations into separate recognitions of 
objects is, like spatial arrangement, related to activity, for all 
those phases of sensory experience will be fused together which 
require one and the same response. Finally, time recognition 
depends on the flux in experience which comes to be recognized 
as a flux not interfering with the permanency of objects. 



Organic retentiveness. Up to this point only casual ref- 
erence has been made to the fact that the nervous system 
is constantly undergoing structural changes as a result of 
use. When an impulse passes from cell to cell, it leaves 
behind a path which makes it easier for some new impulse 
at a later period to pass along the same course. In this way 
it is also made easier for later impulses to be brought 
together. Very soon the effects of past experience become 
so complicated that it is impossible to picture them in 
detail. Thus, when one learns the name of an object, 
there must be traced through the nervous system a series 
of paths which make it possible in all later experience for 
the percept of that object to arouse the tendency to articu- 
late the name. Or, to take another type of example, when 
one has thought of Europe and Asia as parts of a great 
continental mass, it becomes easier in all future experience 
to couple these two ideas in thought. 

The facts referred to in the last paragraph are grouped 
together under such general terms as " organic memory " or 
"retentiveness." It is one of the most important facts about 
the nervous system that it is highly retentive. As a result 
of this retentiveness, present action of any part of the 
nervous system is explicable only in small measure by 
the impressions of the moment. The present impression 
is received into a network of paths which carry the im- 
pulse here and there in accordance with past experiences 
through traces left behind by such experiences. 



Remoter conditions of retention. Considered in a large 
way, all structures of the nervous system are the results of 
past development. The coordinations which the child in- 
herits result from racial experiences, and no individual can 
face the world without reflecting in all of his instinctive 
attitudes the fundamental experiences of his ancestors. 

Ordinarily we do not think of these remoter effects of 
experience. We use the terms " memory " and " retention " 
to refer to those phases of personal experience which we con- 
sciously connect with our own past contact with things and 
people. When the ordinary man uses the term " memory, " 
he thinks of a reinstatement as nearly as possible of some 
situation experienced at an earlier date. One remembers 
what he saw and did yesterday. For the psychologist this 
is only one case of retention and revival. From the doings 
of yesterday there come over into to-day many influences 
which are difficult to observe directly. There is skill of 
hand which is the product of a slow and systematic learn- 
ing process ; there is accuracy of spatial reference which 
makes it possible for the individual to put his hand with 
precision on the object before him or at the right or left. 
There are modes of attention ; there are attitudes of fear 
and anger, all of which come out of the past development 
of the individual but are ordinarily not recognized as due 
to nervous retention. 

Before taking up the cases of memory which are usually 
recognized as coming under that name, it will be well to 
study those less noticed forms of organization which bring 
the past into the present and affect the present without 
being recognized through introspection. 

Instincts. The simplest cases of this type are the instincts. 
As was pointed out in an earlier chapter, every individual 
is born with certain main outlines of his nervous structure 
provided through inheritance, exactly as the other structures of 
his body are provided through inheritance. If an individual 


has arms and legs, he will also have the nerve fibers to 
connect the muscles of these extremities with the spinal 
cord. The structure of the sense organs is also provided 
through inheritance, and, as has been made clear in earlier 
discussions, there is little or no change in the character of 
these organs in the course of individual experience. Inherit- 
ance, however, goes even further than to provide these main 
structures. The central organs themselves are, to some ex- 
tent, mapped out at the beginning of individual life. The 
result of this central organization is that at the time of birth 
the muscles of the body are not merely under the general 
control of the nervous system, they are under the control 
of organized centers which are able, to a certain extent, to 
coordinate the activities of different parts of the body. 

Protective instincts. Illustrations of instincts occur in 
the life of any animal and in the early life of human infants. 
For example, if a young bird hears a loud sound, this sound 
not only discharges itself through the nervous system, but 
because of the internal organization of the nervous system 
the sound will discharge itself into the muscles of the whole 
body in that form of behavior commonly described as feign- 
ing death. The individual bird does not recognize the 
significance or value of its behavior, at least the first time 
it executes it. The act can therefore not be explained as 
due in any way to individual intelligence. Furthermore, the 
same form of action appears in all members of the species. 
The organization which controls the activity has been worked 
out in the course of the experience of the bird's ancestors 
as a form of 'protective movement to be put into operation 
whenever the animal is threatened by an approaching enemy. 
To say that the young bird which performs this movement 
is cognizant of danger and assumes an appropriate attitude 
would be to invert the true relations exhibited in the situa- 
tion. The mode of behavior is immediate and depends 
directly upon the external stimulation plus the inherited 


organization. The attitude of fear results from the action 
which takes place without the animal's control or choice. 
The inner experience of fear is just as much determined 
through heredity as is the ability to hear the sound through 
the ear or the ability to respond to the sound with the 
muscles of the body. 

Food-taking instinct. Other typical illustrations of organ- 
ized instinctive modes of behavior may be drawn from a 
study of the human infant. One of the most fundamental 
instincts of the infant is the instinct of sucking. Any young 
mammal responds to a small object placed between its 
lips by a complex form of reaction which nature has pro- 
vided as the only possible means of supporting the animal's 
life during a period when individual experience is not 
sufficiently mature to guide it in securing its own food. The 
form of consciousness which accompanies this instinctive 
behavior is, of course, a matter of speculation, but it seems 
highly probable that the experience of the infant is one of 
emotional excitement and of satisfaction when the act finds 
some appropriate object on which to express itself. 

Instincts established through selection. The process by 
which the instincts have been evolved is most elaborate. In 
the later stages of animal evolution those members of a 
species which do not exhibit the highly organized instincts 
of protection and food-taking perish. It is easy to see how 
the instincts are perpetuated through natural selection. In 
somewhat the same fashion we can imagine how, through 
a long regressive series, those nervous systems were gradu- 
ally selected which provided the forms of reaction most 
favorable to the preservation of life. 

Delayed instincts common. In treating of human instincts 
the matter is somewhat complicated by the fact that a great 
many instincts are present only in incipient forms at the 
beginning of life and are fully matured at a relatively late 
period. A good illustration of such a delayed instinct is 


found in the tendency of the young child to walk. That 
this tendency is inherited is shown by the fact that it will 
mature, even if there is little or no individual practice. The 
common development of the young child is a mixture of 
maturing instincts and ambitious efforts on the part of 
the child himself and of those surrounding him to hasten 
the development which would naturally come, even if no 
exertions were made in that direction. Certain interesting 
cases are on record which show that children who for one 
reason or another had never made any individual effort to 
mature this mode of activity suddenly exhibited it under 
suitable conditions in a fully developed form. Young animals 
have frequently been experimented upon in a way to show 
that their modes of locomotion are wholly instinctive, even 
though locomotion develops only at a relatively late period 
in life. Thus young birds which have been incubated in 
isolation and have been caged until they reached full 
maturity will fly with the natural mode of flight of their 
species as soon as they are liberated. 

Impossibility of distinguishing instincts from later-acquired 
forms of behavior. As there are instinctive modes of be- 
havior which develop somewhat slowly during the early years 
of life, it is impossible to draw a line and say that every 
form of activity which matures after a certain period is in- 
dependent of direct hereditary organizations. It is equally 
impossible to say, on the other hand, that the inherited 
tracts in the nervous system are in no wise modified in the 
course of individual experience. Indeed, it is always true 
that on the foundation of inherited coordinations there is 
built up a system of refinements and modifications which 
constitute the characteristic mark of the individual. 

Habits from instincts and from independent conditions. 
Instincts are sometimes simplified in the course of use ; at 
other times they are united into larger systems of action or 
are broken up into their elements and recombined into new 


types of composite activity. We turn, then, to the consid- 
eration of these processes of activity which are related to 
instincts merely as outgrowths and may therefore be treated 
as the products of individual experience. Those modes of 
behavior which depend upon individual experience are called 
habits. In order to make clear the relation of habit to in- 
stinct, it should be pointed out that not all habits grow 
directly out of single well-defined instincts. For the pur- 
poses of our discussion two classes of habits may be dis- 
tinguished : first, there are habits which develop out of 
instincts ; second, there are habits which develop by a 
process of selection from among the diffuse activities which 
appear whenever there is no definite mode of instinctive 
behavior which serves as a foundation for development. We 
may refer to these two types of habits as habits developed 
from instincts and habits developed from diffusion. 

Development of habit through conflict of instincts. An 
illustration of a habit developed from instincts is found in 
the case in which a child develops a certain definite attitude 
toward certain animals. This attitude of the child can in 
many cases be shown to have originated out of a conflict be- 
tween two tendencies. There are two fundamental instinc- 
tive tendencies in every child, indeed in every young animal. 
Every young animal tends, on the one hand, to run away 
from any strange or unusually intense stimulation. A large 
object moving toward the eyes, a loud sound attacking the 
auditory organs, or a strange odor or taste will stir up in a 
young animal a mode of action of the protective type. There 
is, on the other hand, among all of the higher animals an 
instinct toward contact with members of the same species 
and with related forms of animal life. Thus, young birds 
naturally tend to keep close to any member of their species 
and to other objects which are in any way similar to mem- 
bers of tjieir own species. So also do young mammals. 
Young puppies and young kittens are extremely fond of 


companionship, and even certain of the more solitary ani- 
mals naturally herd in packs or in small groups, especially 
when young. The human infant exhibits both of the two 
fundamental instinctive tendencies which have just been 
described. When, accordingly, the child is for the first time 
confronted by an animal, its reaction may be one of with- 
drawal or one of friendly contact. Which of the two natural 
tendencies is actually selected will depend upon a variety of 
circumstances. If the instinct of flight or protective activity 
is strong, either because the individual child is disposed to 
react in this way more emphatically than in the direction of 
social contact or if the instinct of protection is rendered 
especially pronounced by some accident of excessive external 
stimulation at the particular moment, then the instinct of 
fear will dominate and the social instinct will be suppressed. 
In such a case the specialized habit will begin to form in 
the general direction of fear. Sometimes the attitude is so 
thoroughly determined by the first contact with the animal 
that all through life the individual tends to follow the initial 
impulse received at the first experience. There are persons 
who have a very strong attitude of fear for cats and dogs, 
which attitude has become a fixed individual habit after 
being selected from among the various possible instinctive 
modes of response which existed through inheritance at the 
beginning of life. 

Nervous development concerned in the selection of in- 
stincts. The nervous mechanism involved in a habit which 
has resulted from selection among instincts is relatively easy 
to explain. We need only to assume that the stimulation 
which is given at the first experience has two possible lines 
of discharge, either one of which would be through a well- 
defined instinctive tract. The conditions of the first en- 
counter carry the stimulation in question into one of the 
two instinctive channels, and thereafter this selected channel 
becomes the natural and easy path of discharge for the 


stimulus whenever it recurs. The habit is, accordingly, de- 
pendent upon individual experience only in the one respect 
that individual experience determines which of the possible 
instincts shall be selected. 

Habit as a modified instinct. A second somewhat differ- 
ent type of derivation of habit from instinct is found in cases 
in which the final mode of activity is not along the line of 
any single instinct, but is a compromise in which one instinct 
is modified by conflict with other instinctive tendencies. 
Suppose, for example, that the human infant who naturally 
tends to be afraid of an animal is encouraged by circum- 
stances to assume a friendly attitude toward the animal of 
which he is naturally afraid. His attitude and mode of re- 
action may be modified to a greater or less extent, so that 
instead of expressing the full tendency of his instinct to run 
away, he may have merely a suppressed internal recoil from 
the animal, while all of his grosser protective movements 
are modified. Many of the human instincts are probably 
thus somewhat reduced in intensity and in their form of ex- 
pression. Darwin argued at length that the expressions of 
human and animal emotions are in many cases simply 
reduced instinctive forms of behavior. Many of the facial 
expressions in human beings are, according to his view, 
remains of early forms of activity in the jaw and mouth 
muscles, which once accompanied real combat. The changes 
in circulation and respiration which come with fear and 
embarrassment are to be regarded as partial expressions of 
certain fundamental instincts. For example, when we are 
frightened there is for an instant a pause in all the internal 
activities preparatory to the violent activities necessary to 
flight, and after this first pause there comes a rapid beating 
of the heart which originally accompanied flight. When in 
mature life one refuses to indulge in flight, he may, never- 
theless, have all the internal activities. If, however, he 
persists in refusing to run, the inherited tendency may, 


through this fact, be gradually overcome even to the point 
of disappearance. 

Importance of heredity in explaining consciousness. Such 
examples as these tend to emphasize heredity. The indi- 
vidual is seen to begin life with a large stock of possible 
habits and instinctive attitudes. His final attitudes are deter- 
mined in kind and degree by the circumstances of individual 
life, but a great number of the fundamental possibilities in 
human nature are given at the beginning of life. We may 
say, therefore, that an individual is born with a large stock 
of attitudes quite as much as with a large supply of organs 
of sense and forms of possible sensory experience. The in- 
herited attitudes are not specific in their application until 
after individual experience has worked out the application, 
but they are native and explicable only in terms that recog- 
nize their fundamentally hereditary character. 

Diffusion a mark of lack of organization. Turning now 
from the habits which are developed through the selection 
and modification of instincts, we come to the habits which 
cannot properly be traced to any single instinct or group of 
instincts. Let us suppose that a stimulus or a combination 
of stimulations is introduced into the nervous system of the 
child but finds no specific channel of discharge open to it 
through inherited organization. This stimulation will pro- 
duce an excitation which will be very widely distributed 
throughout the whole nervous system, because it has no 
specific channel of discharge and because, as free energy, 
it must be transmitted through the nervous system until it 
finds a discharge into the active organs. The stimulation 
will ultimately issue through the avenues of motor dis- 
charge into the active organs of the body, but instead of 
issuing in a well-coordinated series it will be distributed 
diffusely and irregularly and will affect a great number of 
muscles. An example of the diffuse distribution of stimula- 
tion in mature life is seen when one is suddenly startled by 


an unexpected loud noise, and there follows a general con- 
traction of the muscles throughout the whole body. Such a 
strong stimulus breaks over all of the bounds of organization 
in the central nervous system and is distributed diffusely 
throughout the body. A diffuse distribution of the stimula- 
tion is clearly a disadvantage to the individual. The state 
of the organism after the stimulation is such that the indi- 
vidual is not well adapted to his environment, his activities 
are not concentrated in any single direction, and he is alto- 
gether unprepared to meet the future demands which the 
stimulation may impose upon him. Furthermore, it can 
easily be observed that the mental attitude which accom- 
panies such diffuse activity is quite as unorganized as the 
bodily attitude, and this, also, is an intolerable condition for 
any individual. The process of modifying such a diffuse 
reaction, of developing definite and precise attitudes on the 
mental side and well-coordinated movements on the physical 
side, is a long, complex process, carried out by the organism 
and by consciousness with the delays and complications 
which appear in every process of natural development. 

Development of habit from diffusion. If we take a fcrm 
of activity which has little or no instinctive background, such 
as the activity involved in writing, and observe the early 
stages of the effort to develop this type of activity into a 
habit, we discover the characteristics of a diffuse activity. 
It will be found, first, that movement is excessive in both 
extent and intensity. The child who is learning to write 
moves not only the necessary muscles of the fingers and 
hand directly engaged in writing, but the muscles of the 
other hand as well. He also moves the muscles of the face. 
The diffusion of the excitation throughout the whole organ- 
ism is one of the most obvious facts to be observed in such 
a case. In the second place, the elements of movement 
which a^e present are not coordinated into harmonious 
wholes. The various muscular contractions involved in the 


earliest attempts at writing seldom enter into such relations 
that there is economy in their several activities. This will 
be apparent if one observes the way in which the fingers 
and the hand act during the child's formation of series of 
letters. There must always be a movement of the hand 
during writing to carry the fingers across the page. In the 
child's writing the fingers are used as long as they can be 
used without any cooperating hand movement. The hand 
is brought into play only after the fingers have become so 
cramped that they can no longer make lines. When this 
cramping of the fingers reaches such a point that it can go 
no farther, the finger movement is altogether suspended for 
a moment and the hand is moved forward in a distinct and 
relatively separate act. The writing then proceeds as before, 
the fingers being used quite to the exclusion of the hand. 
This obvious lack of combined activity of the hand and 
fingers illustrates a general fact which is also exhibited by 
the incoordination of the learner's several fingers in relation 
to one another. The thumb and first finger do not at the 
outset cooperate with each other in the harmonious way in 
which they should. For example, at the beginning of an 
upward stroke, as in the written letter /, the first finger 
presses downward against the pencil or pen more vigorously 
than is necessary and, as a result, the thumb is called upon 
to do an excess of work in order to overcome the unneces- 
sary downward pressure of the first finger. There is thus a 
lack of harmony and even a certain degree of interference 
in the organs which are directly involved in the activity. 
The explanation of diffusion and incoordination at the be- 
ginning of development is similar to the explanation of the 
general diffusion of the activity throughout the whole muscu- 
lar system in the case of a sudden loud noise. In both cases 
the nervous impulses which excite the muscles do not follow 
definite channels. In the case now under consideration the 
channels are not yet developed, while in the case of the loud 


sound they are not able to confine the strong discharge to 
definite paths. 

Undeveloped movements. Another characteristic of an 
undeveloped movement is one which is closely related to its 
incoordination, and consists in the fact that the various phases 
of movement are all of brief duration, not being united with 
each other into a continuous series. If one examines the 
writing of a child, he finds that the lines, instead of being 
continuous, fluent lines, are made up of short, irregular parts. 
The direction of the movement in these short, irregular parts 
is very frequently away from the general direction which the 
movement should follow. We may say that the movement 
is a succession of efforts to produce the line rather than a 
sequence of coordinated muscular contractions appropriate 
to the general movement. When the movement develops, 
as it does after practice, the different elements are bound 
together in such a way that their sequence cannot be detected ; 
they are no longer separate factors. The adult who begins 
to write the letter / does not make a scries of separate move- 
ments as the pencil is carried along the upward stroke. He 
does, however, make a series of muscular contractions. The 
transition from the irregular succession of separate move- 
ments to a series of contractions constituting phases of a 
single complex activity, which, however, is thoroughly uni- 
fied, results from the coupling together of a series of nervous 
tracts which provide for the proper temporal distribution of 
the motor excitation. 

Diffusion analogous to all forms of overproduction. It is 
clear from the foregoing study of the characteristics of an 
undeveloped activity that nature approaches this problem of 
development in the same way in which all the problems of 
development are approached ; namely, through excessive pro- 
ductions and selection of the proper elements. Since the child 
does not have the proper nervous organization to control 
his movements, nature has provided that he shall make a 


superabundance of movements involving all of the different 
parts of the body, even those which are not directly con- 
cerned in the final activity. If, in this excess of movement, 
certain factors accomplish the end toward which the indi- 
vidual is working, these successful constituents of movement 
will gradually be emphasized and the unsuccessful constitu- 
ents will gradually be eliminated, until finally diffusion gives 
way to a limited number of precise and well-defined combina- 
tions of activity. If the selected factors are repeated together 
a sufficient number of times, the nervous activities involved 
in each particular phase of the movement gradually become 
connected with each other. 

Conscious correlates of habit. The conscious accompani- 
ments of action which has grown habitual are easily described. 
There is a feeling of familiarity when one is trained to respond 
to sensations ; there is a definiteness of discrimination which 
makes one's percepts sure and clear. Too often the psychology 
of habit has been guilty of the statement that habituation leads 
to unconsciousness. This is not the case. When we can deal 
skillfully with any situation, we have an attitude of attention 
and of assurance wholly different from the attitude of indefi- 
nite excitement which accompanies diffusion. The skillful 
man is the discerning man ; his discernments may disregard 
certain factors and emphasize others, but, on the whole, 
he will give attention, to that which is most important in 
guiding action. 

Instinct, habit, and mental attitudes. The reader will be 
able without detailed discussion to see the relation of this 
chapter to the earlier chapter which deals witli mental atti- 
tudes. All mental life exhibits natural likes and dislikes, 
acquired sympathies and antipathies, forms of attention and 
interest. These are related, as was shown before, to modes 
of reaction. We now see how these tastes and interests are 
developed as a part of the individual's adjustment of himself 
to the world. Some tastes are traceable to inherited instincts, 


others to acquired habits, and so on through the list. The 
important fact for psychology is that past experience comes 
over into the present in the form of fundamental attitudes 
and tendencies. The introspective observer is likely to make 
the mistake of thinking that his likes and dislikes are the 
products of his present thinking, when in reality they come 
to him from a remote past, even in some cases from his 
racial inheritances. 

Applications of the doctrine of attitudes to social science. 
What is shown by these few examples is of the greatest im- 
portance for the social sciences. Social life has developed 
innumerable habits in the individual. We pass each other 
on the right ; we accost our friends on the street ; we gather 
about the table and take our food in an orderly way. In these 
and a thousand of the customs of social life we record the 
experience of the past. At the moment we find ourselves in 
sympathy with our surroundings. Indeed, we should be most 
uncomfortable if our surroundings did not call for those forms 
of behavior which are laid down by habit in our nervous sys- 
tems. Personal habits and social customs have thus come to 
be two aspects of a single line of development. Here again 
we are often too much in the midst of the experience itself 
to see how our social attitudes came into being and what is 
their real character. 



Speech as a highly important special habit. Among the 
habits, developed by human beings none is so elaborate as 
speech ; none is so intimately related to the higher levels 
to which human experience attains. Speech is evidently a 
form of muscular behavior, as can be readily observed if one 
notes the movements in the thorax, larynx, and mouth dur- 
ing articulation. So complex, however, are the mental proc- 
esses related to the movements involved in speech that we 
ordinarily overlook entirely the physical side of the process 
and think of speech only as one of the higher forms of 
mental activity. 

Speech and ideas closely interrelated. There would be 
logical justification for a postponement of the discussion of 
speech until after the description and classification of ideas 
and of those thought processes which develop with the 
evolution of language. Speech would then be treated, as it 
is in the thinking of most people, as a product or expression 
of higher intelligence. But speech is more than a product 
of thought ; it is the instrument which makes thought pos- 
sible ; or, differently expressed, it is the kind of reaction 
which is essential to the higher attitudes of discrimination 
and comparison. Just as the processes of perception are 
not merely receptive but involve reactions, so the higher 
thought processes are active and depend for their character 
on those forms of behavior which make up the speech habit. 
We are justified, therefore, in discussing speech before treat- 
ing of ideas, even though we shall have frequent occasion in 



this chapter to refer to the higher mental processes before 
we have described them in detail. 

Speculations regarding the nature and origin of speech. 
Speech has from the earliest history been recognized by man 
as a unique power. It is the distinguishing characteristic 
between Greek and barbarian, between Hebrew and gentile. 
In more emphatic degree, it is the mark of distinction be- 
tween man and his nearest relatives in the animal kingdom. 

Long before there was a science of human nature, man 
speculated curiously as to the source from which language 
came. His first answer was that the Deity gave it to him 
by a special act of creation. 

The special creation theory. The special creation theory 
of the origin of language ignores, however, certain facts 
which are too obvious to be set aside. It ignores the fact 
that animals have the ability to make certain vocal sounds 
which they utilize for purposes of communication with one an- 
other. We cannot explain how it is that animals have modes 
of expression so closely related to human language without, 
at the same time, recognizing the natural origin of language 
itself. Furthermore, the processes of human expression are 
constantly undergoing changes and developments which are 
so natural and so definite in their character that it seems 
probable that language has always been evolving just as it 
is at the present time. If the principles under which lan- 
guage as we know it is developing can be ascertained, it is 
reasonable to project these laws back of the historical period 
and to assume that the beginnings of language were also 
under the regular laws of development. The creation theory 
has therefore gradually given way to various theories which 
attempt to give a naturalistic explanation of language. 

The imitation theory. It has sometimes been held in later 
speculation that language originated from the tendency to 
imitate sounds. This theory, while it would explain certain 
of the special forms of words, cannot give any adequate 


account of the way in which an individual develops the power 
of turning imitation to the special ends of speech. There 
are a number of different animals that are capable of a wide 
range of imitation, but they have never developed a lan- 
guage, as has man. This is clear evidence that the essence 
of language is not to be found in imitation, but rather in the 
use to which the imitative power is put. 

The interjection theory. It has also been suggested that 
language developed out of the interjections which man natu- 
rally used in his most primitive stage of development. If 
he was astonished by any sudden stimulation, he naturally 
gave forth ejaculations in response to the sudden excitation. 
These ejaculations, it is said, came gradually to have the 
power of calling to mind the situations to which they be- 
longed and ultimately became the means of communication. 
Here again the objection to the theory is not that it seems 
improbable that man began with simple forms of expres- 
sion, but that the theory does not explain how these simple 
forms of expression acquired a meaning and importance 
which they did not have at the beginning. What is needed, 
rather than a formal description of the first expressions used 
by primitive man, is a consistent psychological explanation of 
how the ejaculations came to have significance for mental life 
and to serve as the vehicles for elaborate thought processes. 

Roots of language in natural emotional expressions and 
their imitation. The psychological explanation of language 
begins with a general reference to the statements made in 
earlier chapters. Every sensory stimulation arouses some 
form of bodily activity. The muscles of the organs of cir- 
culation and the muscles of the limbs, as well as other 
internal and external muscles, are constantly engaged in 
making responses to external stimuli. Among the muscles 
of the body which with the others are involved in expres- 
sive activities are the muscles which control the organs of 
respiration. There can be no stimulation of any kind which 


does not affect more or less the character of the movements 
of inspiration and expiration. In making these general state- 
ments, we find no necessity for distinguishing between the 
animals and man ; so far as the general facts of relation 
between sensations and expression are concerned, they have 
like characteristics. That an air-breathing animal should pro- 
duce sounds through irregularities in its respiratory move- 
ments when it is excited by an external stimulus, especially 
if that stimulus is violent, is quite as natural as that its hair 
should rise when it is afraid or that its muscles should 
tremble when it is aroused to anger or to flight. 

Imitation. The important step in the development of lan- 
guage is the acquirement of the ability to use the movements 
of the vocal cords for purposes other than those of individ- 
ual emotional expression. The acquirement of this ability is 
a matter of long evolution and depends in its first stages 
upon social imitation. The importance of imitation in affect- 
ing the character of animal behavior appears as soon as ani- 
mals begin to live in packs or herds or other social groups. 

Other imitative communications of animals and man. So 
far as communication through imitation is concerned, there 
is no reason why attention should be confined exclusively to 
the forms of activity which result in sounds. All animals 
imitate the activities of other members of their species on a 
very large scale. The stampede of a herd of cattle is an ex- 
cellent illustration of the importance of the tendency toward 
imitation. The frightened animal which starts the stampede 
does not consciously purpose to communicate its fright to 
the other members of the herd ; it is performing a natural 
act of its individual life. Incidentally, it affects all those 
about it by arousing in them a violent form of imitative 
activity. The stampeding herd may have no consciousness 
whatever of the original cause of fear in one of its mem- 
bers ; the real cause of the stampede and of the resulting 
excitement in the herd is the example of the one frightened 


animal. Thus we see that the activity of an animal takes on, 
because of the reaction of its social environment, a signifi- 
cance which the original act never could have had unless it 
had been imitated. 

Value of sounds as means of social communication. What 
is true of activity in general is true of activities which result 
in sounds. The sound produced by the activities of the vocal 
cords can impress itself readily upon the ears of some other 
animal, more readily by far than the visual impression of 
trembling or of general . muscular tension. If, now, the ani- 
mal which hears the sound has itself produced this sound 
or one closely resembling it in quality and intensity, there 
will be a natural tendency for the sound stimulation to arouse 
in the second animal a sympathetic response. Witness the 
tendency of all the dogs in a community to bark together 
or of all the roosters to begin crowing together when one 
gives the signal. The result of imitating the sound will be 
to throw the imitating animal into an emotional state very 
similar to that of the animal which first made the noise. 
This result will be more likely to follow if the two animals 
are closely related in their organization and types of activity. 
There will be relatively less tendency to sympathize with an 
animal of entirely different organization and habits, for the 
activity aroused through imitation in the listening animal 
will not agree in character with the activity of the animal 
which sets the example. Thus, one can judge from his own 
experience that there is very little possibility of arousing in 
a human being the mental state which appears in dogs or 
cats through imitation of the sounds which they produce. 
In general, imitation of sound is valuable as a means of 
arousing sympathy only between animals sufficiently related 
to each other to have similar modes of producing sound. 

Limitation of forms of animal communication. Given the 
similarity of organization which makes imitated sounds sig- 
nificant, we have a type of communication provided which 


is widely utilized in the animal world. The food calls and 
the danger signals of birds are significant to other members 
of the flock. Such calls have definite natural relations to the 
organized responses of all members of the species. It is to 
be noted that these calls do not constitute a language in the 
sense in which human sounds constitute a language, for the 
bird calls are incapable of conveying definite ideas, such as 
ideas of the kind of food or the particular kind of danger dis- 
covered by the animal which makes the sound. The sounds 
serve merely to arouse certain attitudes. An animal can 
induce in its fellows a tendency to fear and flight by means 
of cries which in the history of each member of the flock have 
been associated with fear, but the animal can go no farther in 
its communications than to arouse emotional attitudes. 

The first stages of human articulation like animal cries. 
There are stages of human infancy which are closely re- 
lated to the stages of animal life thus far described. The 
human infant does not at first make sounds as the result of 
any conscious desire to communicate its feelings to those 
about it, much less does it use its sounds for verbal dis- 
cussion of the details of its conscious experiences. The 
infant makes noises exactly as it swings its arms and legs, 
because the muscular contractions which produce these 
noises are instinctive motor expressions related through 
heredity to the stimuli which arouse them. Later there 
appears a strong tendency to imitate others of its own kind, 
and this imitation may serve to put the infant in some con- 
tact with its social environment and give it a medium of 
communication comparable in character to that which we 
find in animals. This is not language, however, for imitation 
alone is not enough to develop language. Further processes 
must take place before the full development is effected. 

Articulations selected from the sum of possible, activities. 
While irrigation applies to many different forms of activity, 
such as those of the limbs or face, a moment's consideration 


will make it clear that the activities which produce sounds 
have a number of unique advantages as vehicles of imitative 
communication. The ability to produce sounds depends 
largely upon the animal itself and very little upon external 
conditions. Contrast sound with visual impressions. Visual 
impressions are cut off in the dark ; they are cut off by 
intervening objects and by a turning of the head of the 
observer. Sounds travel wherever there is air ; they are as 
easy to produce in the darkness as in daylight; they can 
easily be varied in intensity. For these reasons they come 
to be the chief means of social communication, even among 
the animals. The result is that the vocal cords and the 
ability to discriminate sounds are highly developed long 
before the development of language proper. 

Evolution of ideas and speech. The advance which human 
language makes beyond animal communication consists in 
the fact that human language relates sounds to ideas as 
well as to emotional attitudes. This step cannot be taken 
until ideas are present in the minds of both parties to the 
communication. We find ourselves, therefore, at this point 
involved in a perplexing circle. Human mental processes 
as we know them are intimately related to language. Even 
when we think about our own most direct experiences, we 
use words. Yet these words are not explicable except when 
we assume complex ideational processes as the necessary 
conditions for their development and interpretation. Did 
human mental advance result from the development of 
language, or did language result from the development of 
ideas ? The only answer to this question is that language and 
ideational processes developed together and are necessary to 
each other. 

In describing the first stages of the development of true 
language we may assume, therefore, that both speaker and 
auditor have reached a stage of development where it is 
possible to have higher nervous and conscious processes. 


Such higher processes are to be contrasted with mere emo- 
tional attitudes. For example, if one sees his fellow being 
pointing in a certain direction, there is a strong tendency 
to turn and look in the same direction. There will result 
in this case not an emotion but a common attention to some 
object. The gesture of pointing is, accordingly, a mode of 
communication which rises to a higher level than does the 
cry of fear or the food call. Its development opens the way 
for a higher system of communication. 

Gestures and broad scope of attention. Still higher is 
the gesture that depicts some elaborate act. Thus, when a 
man is hungry he will point to his mouth and make the 
gesture of taking up food and carrying it to his mouth. 
This simple gesture will not be made by an animal, because 
the animal has only a limited range of attention. If the 
animal thinks of food, it cannot entertain any other ideas. 
It spends all its mental energy seeking food rather than 
trying to communicate with some other animal. In human 
life there is breadth of attention exhibited in a gesture. 
The person who makes a gesture includes in his experience 
the person with whom he wishes to communicate, plus the 
idea which is to be communicated. The animal may have 
a simple idea but not the complex of ideas involved even 
in gesture. 

This ability of man to have two centers of attention can 
be explained anatomically by recalling that man has great 
masses of cerebral tissue within which impulses can be 
worked over. The animal has only a little brain tissue, and 
any impulse received in the brain must be discharged very 
soon in the form of a motor impulse. The hungry animal 
must act at once in the effort to remove hunger. Man, on 
the other hand, has enough brain tissue to hold the impulse 
in suspense, unite it with impressions from his fellow beings, 
and act in a complex way with full regard both to his fellow 
beings and to his hunger. 


Gesture, or gesture language as it is called, is thus seen 
to be not merely a complex form of behavior but one which 
expresses a new type of relationship between the reactor 
and his environment. Gesture is a social form of behavior 
involving attention to persons as well as to objects. Indeed, 
gesture supersedes the more direct forms of attack on objects. 

Evolution of gestures in direction of simplification. The 
earliest forms of social communications undoubtedly included 
much gesture if, indeed, they were not limited altogether 
to gesture. The term " natural sign " has been used in 
describing these early gestures. The gesture was so full 
and pantomimic in character that the interpretation was 
almost as direct as in the case of an emotional expression. 
The gesture could be interpreted by anyone who had passed 
through an experience at all like that of the person making 
the gesture. All that we need to assume by way of explanation 
of gesture is the law of social imitation which was stated in 
earlier paragraphs and the higher power of reviving ideas. 

The later development of gesture language brought with 
it a reduction of the gesture so that it became a mere rem- 
nant of the earlier act. This reduction to a simpler act was 
possible within the group of those who had learned to com- 
municate with each other. Thus, instead of requiring the 
full pantomime to communicate the fact that one was hungry, 
it came to be enough that one pointed in the direction of the 
mouth. A mere clue served to arouse the idea. This stage 
is reached when both the parties to the communication have 
developed the power of supplying the ideas needed for 
interpretation to such a high level that it is very easy to 
call out the idea by the slightest hint. 

Speech a highly specialized mode of behavior. This de- 
velopment, which made it less and less important that the 
gesture be a full pantomime, opened the way for a selection 
of certain particular forms of activity which became the 
vehicles of communication and were wholly set aside for 


that purpose. The vocal cords were not available as organs 
for communication of ideas so long as the ideas had to be 
depicted in full by means of elaborately imitable gestures. 
But as the need of gestures diminished and the power of 
supplying ideas increased, the vocal cords proved increas- 
ingly useful as special organs of social communication just 
because they were not otherwise used. The hands which 
were used for communication during the period when ges- 
ture was evolving were in demand for the direct practical 
activities of life. When two individuals wish to communi- 
cate with each other, it is often extremely inconvenient to 
suspend all other activity, to lay down what one may be 
carrying, to come where one may be clearly seen, for the 
purpose of holding a parley. The vocal cords, on the other 
hand, are not required for the practical purposes of life. 
They are easily disconnected in their action from the gen- 
eral mass of the muscles and, therefore, very naturally 
became the organs for a system of social activities. 

One of the most primitive forms of vocal art is the 
work song. This illustrates strikingly the relation of vocal 
reactions to handwork. The workers secured social coopera- 
tion through the song, their hands in the meantime being 
occupied in practical work. 

Consequences of specialization. The fact that speech thus 
separates itself from other forms of bodily activity and be- 
comes a highly specialized system of behavior brings with 
it a number of important consequences. First, it is possible 
for speech to develop to a high level without involving 
the corresponding development of any of the practical arts. 
What is sometimes called pure verbalism may result. Thus 
a student may acquire mere words and not have any power 
of applying the words which he repeats to other forms of 

Second, the specialized character of speech results in 
the sharp differentiation of one local language from that 


of other sections. Ultimately each language grows so far 
from the parent root that it is wholly unintelligible except 
to those who are trained in its special forms. 

Third, there is a possibility that ideas will be attached 
to sounds so loosely and ambiguously that the two parties 
to communication will drift far apart in their interpretations 
while using one and the same sounds. 

Speech an indirect form of behavior. Speech as a form 
of behavior thus lacks that direct relation to the outer 
world which most habits exhibit. It takes on a highly 
artificial character. Its uses are controlled by social con- 
vention rather than by natural necessity. We may therefore 
very properly describe speech as an indirect, conventional 
form of behavior. 

Evolution of writing. The stages of evolution of speech 
which have been described in the foregoing paragraphs 
are exemplified in essentially the same sequence, though in 
slightly different form, in the evolution of the art of writing. 

Writing at first direct in form. The earliest stages of 
writing were those in which pictographic forms were used ; 
that is, a direct picture was drawn upon the writing surface, 
reproducing as nearly as possible the kind of impression 
made upon the observer by the object itself (see Fig. 54). 
To be sure, the drawing used to represent the object was 
not an exact reproduction or full copy of the object, but it 
was a fairly direct image. The visual image was thus 
aroused by a direct appeal to the eye. Anyone could read 
a document written in this pictographic form if he had 
ever seen the objects to which the pictures referred. There 
was no special relation between the pictures or visual forms 
at this stage of development and the sounds used in articu- 
late language. Concrete examples of such writing are seen 
in early monuments, where the moon is represented by 
the crescent, a king by the drawing of a man wearing a 
crown. An example of this stage of writing is also supplied 


by the ancient Chinese forms shown in the upper line 
of Fig. 55. 

Images reduced to lowest terms as powers of reader 
increase. The next stage of development in writing began 
when the pictographic forms were reduced in complexity 
to the simplest possible lines. The reduction of the picture 
to a few sketchy lines depended upon the growing ability of 
the reader to contribute the necessary interpretation. All 
that was needed in the figure was something which would 


FIG. 54. An Ojibwa love letter, recorded and explained by Garrick Mallery 
in the Annual Report of the Bureau of Ethnology, 1888-1889, p. 363 

The writer, a girl of the Bear totem, &, summons her lover, who belongs to the 
Mud Puppy totem, d, along the various trails indicated, to the lodge, c, from which 
the beckoning hand protrudes. The inclosed figures at /,_/, and k are lakes. The 
crosses indicate that the girl and her companions are Christians. "The clear indi- 
cations of locality," writes Mallery, " serve as well as if in a city a young woman had 
sent an invitation to her young man to call at a certain street and number " 

suggest the idea to the reader's mind. The simplification 
of the written forms is attained very early, as is seen even 
in the figures which are used by savage tribes. Thus, to 
represent the number of an enemy's army, it is not neces- 
sary to draw full figures of the forms of the enemy ; it is 
enough if single straight lines are drawn with some brief 
indication, perhaps at the beginning of the series of lines, 
to show that these stand each for an individual enemy. 
This simplification of the drawing leaves the written sym- 
bol with very much larger possibilities of entering into 


new relations in the mind of the reader. Instead, now, of 
being a specific drawing related to a specific object, it 
invites by its simple character a number of different inter- 
pretations. A straight line, for example, can represent 
not only the number of an enemy's army, but it can rep- 
resent also the number of sheep in a flock, or the number 
of tents in a village, or anything else which is capable of 
enumeration. The use of a straight line for these various 
purposes stimulates new mental developments. This is 
shown by the fact that the development of the idea of the 


FIG. 55. Ancient and modern Chinese writing 

The upper line shows ancient forms of Chinese writing ; the lower line shows the 

derived modern forms. Reading from left to right, the characters signify "sun," 

"moon," "mountain," "tree" (or "wood"), "dog" 

number relation, as distinguished from the mass of possible 
relations in which an object may stand, is greatly facilitated 
by this general written symbol for numbers. The intimate 
relation between the development of ideas on the one hand 
and the development of symbols on the other is here very 
strikingly illustrated. The drawing becomes more useful 
because it is associated with more elaborate ideas, while the 
ideas develop because they find in the drawing a definite 
content which helps to mark and give separate character to 
the idea. Striking examples of the simplification of form 
in order to facilitate the writing of symbols are shown in 
Figs. 55 and 56. 


Written symbols and their relation to sounds. As soon 
as the drawing began to lose its significance as a direct 
perceptual reproduction of the object and took on new 
and broader meanings through the associations which at- 
tached to it, the written form became a symbol rather 
than a direct appeal to visual memory. As a symbol it 
stood for something which, in itself, it was not. The way 


FIG. 56. Derivation of the Roman letter M from the ancient Egyptian 
hieroglyphic owl 

The four forms in the upper part of the figure are Egyptian forms. The first on the 
left is the usual hieroglyphic picture of the owl, or, as it was called in the Egyptian 
language, mulak. The three remaining upper forms are found in the writings of the 
Egyptian priests. The first form on the left of the lower series is an ancient Semitic 
form. Then follow in order an ancient Greek form and two later Greek forms. 
(From 1. Taylor's "The Alphabet," pp. 9, 10) 

was thus opened for the written symbol to enter into rela- 
tion with oral speech, which is also a form of symbolism 
(see Fig. 56). Articulate sounds are simplified forms of 
experience capable through association with ideas of ex- 
pressing meanings not directly related to the sounds them- 
selves. When the written symbol began to be related to the 
sound symbol, there was at first a loose and irregular relation 
between them. The Egyptians seem to have established 


such relations to some extent. They wrote at times with 
pictures standing for sounds as we now write in rebus puz- 
zles. In such puzzles the picture of an object is intended to 
call up in the mind of the reader not the special group of 
ideas appropriate to the object represented in the picture 
but rather the sound which serves as the name of this object. 
When the sound is once suggested to the reader, he is sup- 
posed to attend to that and to connect with it certain other 
associations appropriate to the sound. To take a modern 
illustration, we may, for example, use the picture of the eye 
to stand for the first personal pronoun. The relationship 
between the picture and the idea for which it is used is 
in this case through the sound of the name of the object 
depicted. That the early alphabets are of this type of 
rebus pictures appears in their names. The first three 
letters of the Hebrew alphabet, for example, are named, 
respectively, aleph, which means "ox," beth, which means 
"house/ 1 and gimmcl, which means "camel." 

The alphabet. The complete development of a sound 
alphabet from this type of rebus writing required, doubt- 
less, much experimentation on the part of the nations 
which succeeded in establishing the association. The Phoe- 
nicians have generally been credited with the invention of 
the forms and relations which we now use. Their contri- 
bution to civilization cannot be overestimated. It consisted 
not in the presentation of new material or content to con- 
scious experience but rather in bringing together by asso- 
ciation groups of contents which, in their new relation, 
transformed the whole process of thought and expression. 
They associated visual and auditory content and gave to 
the visual factors a meaning which originally attached to 
the sound. Pictures thus came to mean sounds rather than 
objects (see Fig. 56). 

Social motives essential to the development of language. 
The ideational interpretations which appear in developed 


language could never have reached the elaborate form 
which they have at present if there had not been social 
cooperation. The tendency of the individual when left to 
himself is to drop back into the direct adjustments which 
are appropriate to his own life. He might possibly develop 
articulation to a certain extent for his own sake, but the 
chief impulse to the development of language comes 
through intercourse with others. As we have seen, the 
development of the simplest forms of communication, as 
in animals, is a matter of social imitation. Writing is also 
an outgrowth of social relations. It is extremely doubtful 
whether even the child of civilized parents would ever have 
any sufficient motive for the development of writing if it 
were not for the social encouragement which he receives. 

Social system as source of the form of words. Further- 
more, we depend upon our social relations not merely for 
the incentives to the development of language but also for 
the particular forms which oral and written language shall 
take. It is much more convenient for a child born into a 
civilized community to adapt himself to the complex symbol- 
ism which he finds in the possession of his elders than to 
develop anything of the sort for himself. It is true that 
tendencies exist early in life toward the development of 
individual forms of expression. A child frequently uses a 
certain sound in a connection which cannot be explained 
by reference to social usage. It may be a purely individual 
combination, or a crude effort to adopt something which 
has been suggested by the environment. This tendency to 
give sounds a meaning might prove sufficient to work out 
a kind of language, even if the individual were entirely 
isolated from his fellows ; but the natural tendencies are 
very early superseded by the stronger tendencies of social 
imitation, and in the end the social system completely 
dominates individual development, dictating in all cases the 
forms of words. 


Social usage and the domination of individual thought. 

In adopting the forms of expression used by those about 
us, we are led to take up certain general social forms of 
thought which ultimately control the whole mental life. The 
effect of this social influence is so far-reaching that it is 
quite proper to say that an individual is, in a very large 
measure, the creation of his social relations, at least in the 
higher phases of his mental life. The fundamental forms 
of direct activity, which constitute the personal habits by 
which we have succeeded in adapting ourselves to the 
demands of the physical world, are to a certain extent 
unsocial. They are, to be sure, alike in different individuals 
because they have grown up, as was shown in our earlier 
discussion, under the demands of a common physical 
environment. Our forms of space perception, for example, 
are not the creations of our own individual caprice but 
rather the arrangement which we have given our sensory 
experiences in our effort to fit ourselves to a world which 
dictates these space relations to us. Since we have all grown 
up in the same space world, our space ideas are alike. 
The community of social ideas expressed in language is of 
a different type. Even the direct, relatively unsocial forms 
of perception are influenced by these higher social forms 
of thought. If, for example, there is no word in a certain 
social environment for long spatial distances except a word 
which refers to a certain number of days' journeys, it is not 
likely that the individual will feel any tendency to discrimi- 
nate fifteen miles from seventeen. His attitude in this 
matter will be determined by the attitude of his social 
environment, and he will neglect in his thought, as do 
those about him, the finer details of distance. Similarly, if 
there are no names for certain forms of property rights, it 
is not likely that the individual will, of his own initiative, 
recognize these forms of right as belonging to those who 
constitute the social group with him. 


Social ideas dominate individual life. The history of 
thought has been, in large measure, the history of the 
development of certain social ideas which could be marked 
with definite names and made subjects of thought, because 
they were so marked. Consider for a moment the difficul- 
ties which would be experienced in conducting any train 
of thought with regard to the forces of physical nature if 
there were no names for the different forces and no fully 
developed definitions to give each name clearly recognized 
character. If it is true in a general way that general ten- 
dencies of thought have been dependent upon the develop- 
ment of words to express ideas, it is still more true in the 
case of the individual that his mental tendencies are very 
largely determined by the forms of social thought expressed 
in words. A child who has had his attention called to 
certain colors and who is, at the same time, given a name 
for these colors is more likely to identify them in later 
experience than if no name had been given. The name 
serves as an incentive to the concentration of attention 
upon a particular phase of experience which would otherwise 
be lost in the general mass of sensations. Without the 
word the possibility of dwelling upon the single phase of 
experience in thought would be small. This is the reason 
why the retention of facts in memory is so closely related 
to the naming of objects. 

Experimental evidence of importance of words. Some 
experimental evidence can be adduced to show that names 
are of great importance in this respect. If one is confronted 
with a large number of pieces of gray paper ranging from 
black to white, and is asked to discriminate as many of 
these different grays as he is able to recognize with certainty, 
it will be found that he can distinguish ordinarily about five 
classes of gray shades. He can distinguish the very dark 
from those which are medium dark, the very light from 
those that are medium light, and he can place between the 


dark and the light grays a middle shade which he is not 
disposed to classify as either light or dark. Beyond this 
fivefold discrimination he will find that he is very uncertain. 
If, now, after making this test under ordinary conditions, 
the individual is allowed to examine the various shades of 
gray and to adopt a series of names or numbers for them, 
it will be found that he can notably increase the range 
and certainty of his discrimination. The names furnish, as 
stated above, definite means of concentrating attention upon 
slight differences which existed from the first but were not 
noted in experience. Furthermore, when these slight differ- 
ences have been discriminated and marked by the attachment 
to them of definite names, they become permanent additions 
to the individual's equipment and can be retained more easily 
than they could be as mere unnamed sensation qualities. 

Number terminology as a device for recording posses- 
sions. One of the best illustrations of the significance for 
mental life of the creation of a terminology is found in the 
ease with which a developed individual uses numbers. In 
general, it may be said that primitive languages have only 
a very meager number terminology. Savage tribes have 
frequently been known to have no number terminology 
reaching above ten, and in some cases tribes have been 
reported with a number terminology not reaching beyond 
three. There are certain forms of direct perceptual experi- 
ence which can be utilized up to a certain point instead of 
the developed number system which we now have. If a 
herdsman has a herd of cattle for a period long enough to 
become acquainted with its individual members, he can 
recognize the size of the herd by recalling the individuals 
which make it up. If one has material possessions which 
can be heaped together, he will come to estimate his wealth 
directly through the general impression made upon him by 
collecting all of his wealth at a single point. As soon as 
the direct recollection of each individual possession came, 


in the development of human wealth, to be too cumbersome 
a form of representation, and the collective image became 
too vague to be relied upon, man naturally endeavored to 
devise a method of recording his property and retaining it 
in consciousness in some simplified form. Instead of trying 
to remember every one of his possessions, he adopted some 
system of tally. At first he began counting off on his 
fingers each different article which he wished later to be 
able to recognize, or he adopted in some cases one of the 
more elaborate methods found among savages who use 
pebbles or shells. The Latin root which appears in our 
word "calculate" and all related words is the word for 
pebble, and indicates that the early forms of computation 
among the Romans consisted in the use of pebbles. 

Symbols for groups of tallies. As soon as the system of 
enumeration became complex, there naturally arose the 
necessity for grouping the tallies so that they could be 
easily surveyed. The method of grouping the tally marks 
in a system convenient for recognition is suggested by the 
five fingers on the hand, and this is often adopted, even by 
savage peoples. A clear indication that this grouping ap- 
peared in the natural tally systems can be seen in the symbols 
used by the Romans to indicate numbers, for in this system 
the number five and the number ten are crucial points in 
the notation, and show the adoption of a new group symbol 
to include many individual symbols in a more compact form. 

Parallel growth of number names and system of ideas. 
As the number system was worked out into a system of 
major and minor groups there was a tendency to develop 
a system of articulation directly related to the tally system. 
Number of the primitive tally form probably developed just 
as did writing, without reference to speech. The creation 
of words which should express number was slow, as indi- 
cated by reference to savage language, because in this case 
the symbolical system needed to develop to a high degree 


before the demand for corresponding articulation was felt. 
As soon as the demand for articulation became sufficiently 
pressing, the words appeared, and they show distinctly in 
their character the tendency toward groups. Further than 
this, the names for successive tallies came to be the means, 
not only of referring to individual marks but also of refer- 
ring to the serial arrangement of these marks. Thus, the 
names "one," "two," "three," etc. are not significant 
merely as names of tally marks ; they have also each its 
special significance as the name of a special position in 
the total series. 

Development of arithmetic depends on an appropriate 
system of numerals. The advantage to the child who finds 
a complete number terminology developed is very great. 
The more perfect this terminology for purposes of express- 
ing quantitative relations, the more complete and rapid will 
be his initiation into the forms of thought which the 
terminology expresses. The historical illustration of this 
fact is to be found in the acceptance by European nations 
of a system of notation which was imported from the East 
in the Renaissance period. The written number symbols 
which had been used by the Romans were crude and 
rendered any forms of arithmetical manipulation extremely 
difficult. The Arabic system was so much more complete 
and economical that it immediately took the place of the 
older and cruder symbolism. How long it would take an 
individual child to acquire independently anything like the 
mathematical ability which, with the aid of his social en- 
vironment, he acquires through the adoption of the developed 
Arabic number system can hardly be imagined. Certain it 
is that his forms of thought are now dominated by the 
social system into which he is born, and this system was 
in turn borrowed in toto from non-European nations. 

Social world unified through common forms of thought. 
There is in this acceptance of the social system not only an 


economy which operates to the advantage of the individual, 
but there is the additional fact that the individual becomes 
thereby a part of the social whole in a fashion which is sig- 
nificant for society as well as for himself. We are bound 
together as intelligent beings by the common systems of 
tradition and language to a degree which makes us no longer 
centers of merely individual adaptation, but rather parts of 
a general organization which has a certain unity and exer- 
cises a dominating influence over many individuals. This 
social 11 unity perpetuates customs and practices so that we 
have, in addition to the bodily structures which we inherit, 
a social heredity which guides us in the activities of per- 
sonal life. Language is the chief medium for this social 

Changes in words as indications of changes in individual 
thought and social relations. It is in connection with the 
development of social institutions that we find the most radical 
changes in human language. If an individual comes upon a 
new idea and coins a new word for its expression, the new 
word gains standing and comes to be a part of the perma- 
nent language of the community only when others feel the 
same necessity as the inventor of the word for this new 
means of expression. When, therefore, we have a long his- 
tory of variations in any word we may depend upon it that 
there has been a corresponding series of social as well as 
of individual experiences related to the word. The detailed 
history of words is a detailed history of individual mental 
attitudes toward the world, and at the same time a detailed 
history of the social relations in which individuals have joined. 

Illustration of change in words. It will not be in place in 
this connection to enter into any elaborate linguistic studies, 
but one illustration may be used to indicate something of 
the character of the psychological and social study which 
grows out of the history of words. In his " English Past 
and Present," Trench gives an account of the development 


of the word "gossip." This word was originally used at bap- 
tismal ceremonies and referred to the sponsor who stood for 
the child in a way analogous to that in which to-day the god- 
parent stands as sponsor for the child. The first three letters 
of the word " gossip " arc derived directly from the word 
" God," and the second part of the word, namely " sip," is 
a modification of the word " sib," which is even now used 
in Scotland to indicate a relative. When the social institu- 
tion of baptism was a matter of larger community signifi- 
cance than it is to-day, the word was needed to express the 
relationship of the individuals involved in the ceremony ; 
but being a general form of expression rather than an image 
of a particular individual, it came easily to refer to other 
phases of social contact than that which was primarily thought 
of in connection with the baptismal ceremony itself. The 
worthy sponsors of the child unquestionably indulged, even 
in the early days of the ceremony, in certain exchanges of 
information with regard to other members of the community, 
and this social function which the individual served was very 
readily connected with the word coined to refer primarily to 
the religious function. As the religious ceremony came to be 
less and less elaborate, and there was a decreasing demand 
for reference to the religious function, the word gradually 
drifted over to the second phase of meaning. It is probably 
true that the aberration of form, which appears in softening 
the d in " God " to an s, made this transfer of meaning easier. 
Indeed, as we have seen at various points in our discussions, 
words become true symbols only because they are simplified 
so as to take on easily new types of relation. Thus, the 
word " gossip" ultimately lost its original meaning and came 
to signify something which it signified only very vaguely to 
the minds of those who first used it. Furthermore, it is 
clear that this transfer of meaning is directly related to the 
development of the social institution with which the word 
was connected. The mental attitude ef the individual who 


uses the word to-day and the social character of the insti- 
tution are both entirely different from the attitude and 
institution of earlier times. 

Words as instruments of thought beyond immediate ex- 
perience. Other illustrations of the developments which take 
place in language can be found in the introduction of new 
words with new inventions and new discoveries in science, 
Once the habit of using words is thoroughly established in 
a community or individual, it furnishes an easy method of 
marking any experience which it is desired to consider apart 
from the general setting in which that experience appears. 
If to-day a civilized individual wishes to think of certain 
relations such as the physical force of gravity, or the eco- 
nomic facts of value, and to consider the bearings of the 
factors which enter into these relations, he will devise some 
word or phrase by which to mark the relations and hold 
them clearly before his thought while he considers all of the 
facts. There comes to be thus a system of experiences which 
we are justified in describing as constructed in consciousness 
for the purpose of guiding attention ; these constructs have, 
as contrasted with ordinary mental images, very little con- 
tent. Indeed, the reduction of the content of thought to the 
lowest possible minimum is the tendency of all mental evo- 
lution. The child has undoubtedly a more concrete imagery 
than the adult. The adult finds as he learns to use words 
fluently that the imagery which at first was necessary to ex- 
plain them falls away. The result is that great ranges of 
thought can be much condensed ; as, for example, when all 
the cases of falling bodies are thought of at once under the 
single term " gravity/' In the discussion of habits it was 
shown that as experience becomes more completely organ- 
ized into habits, the memory content and even the sensory 
contents receive less attention. An organized attitude is sub- 
stituted for a complex of content factors. In somewhat 
analogous manner, words may be regarded as means of 


epitomizing consciousness, while they permit the highest 
type of ideational elaboration of experience. The widest 
variety of content factors may be related to words ; that is, 
the use of a word is often cultivated under the guiding in- 
fluences of concrete content, as when the child builds up 
the idea of animal through direct perceptual contact with 
dogs and horses. After a time the concrete memory images 
attached to the word fade out and leave the word as a 
substitute, as a minimum content to which (as when the 
man condenses his whole attitude towards all kinds of ani- 
mals into a single compact experience) an elaborately organ- 
ized meaning may attach. 

Images and verbal ideas. When, therefore, we ask what 
it is that a person thinks of in his use of a word, we shall 
certainly go astray if we attempt to answer that the word 
calls up all of the concrete experiences with which it has 
been connected and with which it may be connected. For 
example, let the reader ask himself what presents itself in 
consciousness when he sees the word " animal." It would 
be still better if, instead of choosing some word thrown into 
the text as an isolated illustration, we should ask the reader 
to give an account of the mental experiences through which 
he passed when he observed one of the words that came 
in the course of the general discussion. For example, what 
was called up a moment ago when the eye passed the very 
definite word "text" ? The answer to these questions with 
regard to the content of consciousness at the moment of 
recognition of words will certainly not be that the mind is 
filled with trains of concrete images. 

Mental attitudes as characteristic phases of verbal ideas. 
The consciousness of a word has sometimes been described 
as a feeling or an attitude, and such a description as this 
unquestionably comes nearer to the truth than does the 
explanation of meaning through images, which has some- 
times appeared in psychological discussions of this matter. 


A general term such as " animal " or " text " turns the 
thought of the reader in one direction or the other without 
filling the mind with definite contents. The content of experi- 
ence arises rather from the total phrase or sentence ; the 
single word indicates only the direction in which this content 
is to be sought, or in which it is to be applied in some future 
stage of mental activity. For example, if I say that all ani- 
.mals are subject to man's dominion, there is much more of 
attitude in the whole experience than there is content. We 
look down upon the animals ; we feel their inferiority ; we 
recognize ourselves as above them. The attitude of mind 
experienced is the all-important fact. There is an experi- 
ence of personal elation, which may perhaps be worked out 
into imagery, if one contemplates it long enough. Thus, 
one may turn the thought into images by thinking of him- 
self for the moment as the representative man looking down 
upon the animals gathered as he saw them in childhood in 
some picture of Adam naming the animals. .But all this 
concreteness in one's description of the animals and of him- 
self is recognized as too picturesque to be true to ordinary 
experience. We can stop and fill out the attitude with ap- 
propriate imagery if we like, but we do not ordinarily do 
so. The truer statement is that the idea comes as a single 
simple attitude and prepares one to go on from a position 
of superiority to some appropriate sequent relation. The 
value of the words lies in the fact that they carry experi- 
ence forward, furnishing only so much content as is neces- 
sary to support thought without overloading experience with 
all the detail. 

Other illustrations of thought relations. Again, take 
another illustration which shows that there may be nicety of 
shading in our thought relations without much content. If 
we use such a word as " savage," we are likely to take an 
attitude of superiority somewhat analogous to that taken 
toward the animals, but flavored more than the former idea 


with a concession of equality. If we speak of higher beings, 
such as angels, we assume an entirely different attitude, 
without necessarily giving ourselves the trouble to fill in 
any definite content. Indeed, the content of any thought 
referring to the higher beings is recognized everywhere as 
more or less of a makeshift, in that we fill in the unknown 
with such images as we can borrow from ordinary life, the 
images being symbols, not true representations. 

Concrete words. All this has been expressed by certain 
psychologists in the statement that general ideas are in es- 
sence nothing but dispositions toward activity. Here we have 
a formula which is very closely related to the formula which 
we derived in our discussion of the development of percepts. 
There are, undoubtedly, direct motor habits and consequent 
attitudes in connection with many concrete words. It is, on 
the other hand, probably not true that the bodily attitude as- 
sumed when we think of the word " animal" is anything like 
a complete bodily attitude such as would be assumed in the 
presence of animals in concrete experience. The mental 
attitude aroused by the word probably has as its direct physi- 
ological parallel a bodily movement which is a much-reduced 
resultant of earlier direct attitudes. It is in its present form 
merely a faint reverberation, significant not for direct adap- 
tation but merely as a step in the development of a general 
and perhaps very remote form of activity. The present atti- 
tude is one of those indirect forms of human adjustment 
which render the experience of man freer and more idea- 
tional than the experience of the animals. The bodily move- 
ment in such cases is symbolical and transient, assumed 
merely for the sake of carrying the individual forward into 
a more complete state which lies beyond. 

Examples of words arousing tendencies toward action. The 
matter may be made clear by considering what happens when 
by means of words one is told that he is to go first to the 
right until he reaches a certain place, and is then to turn 


toward the left and go straight ahead. There are clearly cer- 
tain tendencies toward direct bodily movements aroused by 
the words " right " and " left " and " straight ahead." These 
tendencies toward movement, it is true, are not significant as 
present adaptations to the environment ; they are significant 
merely because they give the thinking individual a certain 
tendency, which may, indeed, work itself out later in a much 
more fully developed and concrete form, but is at present a 
kind of suppressed, incipient form of action. If one has 
thought out a series of movements toward the right and left, 
he will have developed within himself a form of behavior 
which, on the presentation of the appropriate stimulation in 
the form of the signpost or building at which he is to turn, 
will serve as a sufficient preliminary organization to arouse a 
significant and concrete form of behavior. The preliminary 
thought attitude and faint bodily expression serve, therefore, 
in a tentative way to aid subsequent direct adaptations. 

Abstract words. If, now, we choose as our illustration 
not words of direction but abstract phrases, such as the 
phrases by which men are exhorted to patriotism, obviously 
the emotional stirring which one feels as the result of these 
exhortations is by no means adequate to explain the true sig- 
nificance of the word " patriotism." A man cannot become 
truly patriotic by going through the inner stirrings which this 
word arouses. Indeed, in not a few cases vague emotional 
responses check rather than promote the development of true 
interpretations because the vague response satisfies the need 
of the mind for experience but gives no complete or adequate 
content. The trouble with the emotional response lies not 
in the fact that it is emotional but in the impossibility of its 
expressing fully the whole significance which the word must 
carry. Such an abstract term as that under discussion can be 
made potent for direct bodily organization only when it is 
supplied through proper settings with some definite and final 
purpose of an active kind. To be truly patriotic one must be 


aroused to some definite form of public service. The final 
purpose will then be like the concrete words " left " and 
" right." The abstract word taken alone is the expression of 
a relation. If it is treated as a final factor of experience, it 
will dissipate itself in vague emotional reactions. 

To take still another illustration : If in the course of a 
scientific discussion one is told that a certain problem needs 
very much to be investigated, the word " problem " will arouse 
within the individual some kind of a responsive attitude which 
can be described in a general way as an attitude of hesitation, 
of turning hither and thither in the search for a solution. But 
the conscious process will be more than the attitude of hesi- 
tation and turning, for it will have a form and significance 
determined by the whole train of ideas into the midst of which 
this attitude of hesitation and turning is injected. Thus, if 
the problem is in geology, the attitude of inquiry will be very 
different from that which would be assumed if the train of 
thought related to astronomy. We may therefore speak of 
the attitude aroused by the word "problem" as wholly rela- 
tional in its character. Another way of expressing the matter 
is to say that the attitude is in the world of ideas for the time 
being rather than in the world of practical adjustments. We 
mean by such statements as these that the attitude is merely 
a temporary step in the process of ideational organization ; it 
is not an immediate reaction on any object. It is an indirect 
and elaborate phase of adaptation ; it has value and signifi- 
cance because of the turn which it gives to the ideational 
process rather than because of the concrete imagery or 
reaction to the world of things. 

Contrast between concrete images and abstract ideas. The 
indirectness of verbal forms of consciousness and of the re- 
lated nervous processes involves, as has often been noted in 
discussions of language, certain dangers of possible malad- 
justment. Concrete images and direct forms of experience 
cannot, because of their limited nature, be turned in very 


many directions. Verbal ideas, on the other hand, espe- 
cially if they are abstract, are capable of a great variety of 
connections because they are so meager and schematic in 
individual content. 

Besides this, there is a disadvantage in the use of ab- 
stract terms in that two individuals, while they may start 
with the same general tendency of attention, may, in the 
course of the use of the words, drift apart, without being as 
clearly conscious of their divergence from each other as they 
would be if they dealt constantly with concrete percepts. It 
is a much more definite method of interchanging ideas to 
demonstrate the objects themselves, or to demonstrate some 
concrete representations of the objects, such as pictures or 
models. If one does not have pictures or models, he natu- 
rally tries to correct the errors which are likely to creep in 
when he is using words, by calling up from time to time as 
concrete an image in the mind of his listener as it is possi- 
ble to evoke by the use of words. We all of us feel the relief 
in any continued discourse when a figure of speech, or an 
illustration, is used. The figure of speech gives us a fairly 
concrete image with which to deal. The image in this case 
may be remote from the immediate subject of thought, it may 
be related to the present discussion only as a kind of rough 
analogy, but the presence of some characteristic which illus- 
trates and renders concrete the abstract discussion is a relief 
in the midst of abstract relational terms and furnishes the 
means of correcting possible tendencies toward divergence 
of thought between the speaker and the listener. An illus- 
tration is even more definite in its character, and so long as 
it calls up in the minds of the speaker and listener the same 
kind of concrete images, it is a direct corrective of the possible 
looseness of verbal thought and verbal communication. 

Particular images as obstructions to thought. How far 
one should be picturesque in his language, and how far one 
should, on the other hand, use terms which are not related 


to definite mental pictures, is a matter which must be deter- 
mined by the demands of the particular situation at hand. It 
would be quite impossible in any generalized science like 
physics continually to deal with concrete illustrations. If the 
scientist speaks, for example, of the general law of gravity, 
he cannot be dealing with all of the specific cases of gravity 
known to his experience, nor can he feel himself bound to a 
single illustration. He may come back to the single illustra- 
tion in order to hold his verbal idea true to the concrete facts, 
but he should cultivate the ability to get away from the con- 
crete cases into the wider sweep of thought which is covered 
by the general word. 

Ideas or indirect forms of experience characteristic of man. 
In concluding this discussion of language it will be well to 
reiterate that human life has taken on, through the develop- 
ment of indirect modes of consciousness and behavior, an 
aspect which differentiates it altogether from the life of ani- 
mals. The consequences for human nature of the evolution 
of a mode of reaction such as speech is, are unlimited in im- 
portance. The full significance of this unique mode of be- 
havior will become increasingly apparent as we canvass in 
detail the problems of ideation and abstraction. 


The problem of describing ideas. Throughout the last chap- 
ter reference was made to ideas without any effort to describe 
in full these important phases of experience. It now becomes 
necessary for us to take up the treatment of ideas and of the 
complex processes of thought which are made up of ideas. 

The way has been prepared for this discussion by the con- 
clusions reached in all earlier chapters. Let us review briefly 
the essentials of our earlier studies. First, animals develop 
inner states in their efforts to respond to sensory stimuli. 
Second, the higher animals become increasingly able to carry 
on elaborate internal readjustments. Corresponding to these 
elaborate readjustments are certain complexes of sensations 
and certain attitudes which gradually grow more and more 
highly differentiated. Third, the inner organization of man 
and his closest relatives in the animal world is such that ex- 
perience is progressively recorded in the form of habits of 
reaction and corresponding mental states. 

We are now ready to ask what is the form of this inner 
enriched mental life which man develops in the course of 
experience. Our popular language is well supplied with words 
referring to these products of experience. We say that man 
stores up in memory ideas and thoughts. We speak of re- 
calling the past, of images in the mind, of an inner world 
of thoughts and thought relations. 

Ideas not derived from present impressions. In all such 
phrases as the above there is a sharp contrast between 
present sensory impressions and the experiences which are 



brought over from the past. There is also a recognition of 
the overwhelming volume of past experiences. The indi- 
vidual faces the world of the present moment with a mind 
set and prepared through long training. What we call 
intelligence is not the impression of the moment but a 
body of experiences drawn out of the past. 

Ideas as revivals. Let us consider some of the simplest 
types of ideas. Tf one closes his eyes and thinks of the 
scene which a moment before impressed itself upon his 
vision, he will recognize that his consciousness is filled with 
a substitute for direct visual sensations and percepts ; this 
substitute is called a memory image. When one thinks of 
an absent acquaintance, the memory image may contain 
factors which are substitutes for direct auditory impressions 
of the voice. When one thinks of a rough surface without 
touching it, the image contains substitutes for tactual factors 
and their perceptual organization. These illustrations serve 
to emphasize the scope of the word " image, " which it will 
be seen is used not merely for vision but also for all spheres 
of experience. 

Advantages of relative independence of sensory impres- 
sions. Before taking up any of the details regarding the 
character and laws of memory images, it will be well to 
dwell briefly upon the great advantage to the individual of 
possessing these substitutes for direct impressions. The 
mind supplied with memory images is relatively independent 
of contact with objects ; the images may serve as the basis 
for attitudes and for reconstructive organizations which may 
be of the highest significance in individual life. A common- 
place illustration of this advantage is seen whenever one 
runs over in his mind the various places in which he has 
been and where he might have left a lost object. More 
complex illustrations may be drawn from the mental activi- 
ties of an inventor who thinks out many combinations, thus 
*sing the images in consciousness as substitutes for real 


objects. To be sure, there are certain disadvantages which 
connect themselves with these advantages. The inventor can 
make more mistakes in this imagery than he could if he 
tried to fit together real things, and one's false memory of 
where he left his property may lead him far astray. But 
taken in the large, the freedom from the necessity of always 
waiting for direct impressions is one of the great superiorities 
of the higher forms of mental life. 

Individual variations in imagery. One of the most im- 
portant statements to be made in the description of memory 
images is that different individuals show great differences in 
the character and vividness of their memory images. Some 
years ago Galton asked a number of individuals to test their 
mental imagery by calling up as definitely and fully as possi- 
ble the familiar objects of the breakfast table. After the 
memory image had been called up, the observer was requested 
to state how clear the mental image was in color and form 
and other characteristics. Some of the observers said that 
they recalled objects with a vividness and detail altogether 
comparable to their perceptual experience. These Galton 
called good visualizers. Others described their memory 
images as extremely vague and hazy. Still others, who were 
between the extreme classes, stated that their mental images 
were restricted in extent and were relatively fainter than the 
percepts themselves but, nevertheless, fairly comparable in 
general character to direct sensory experiences. Galton 's 
tests have frequently been repeated, and his results have 
been fully corroborated. Furthermore, it has been found 
that persons who have faint visual images have, in some 
cases, vivid auditory images. Some persons have vivid tac- 
tual imagery or vivid memory of movements. The blind, 
for example, can have no visual memories ; their memory 
consciousness must therefore be filled by a totally different 
type of content from that which exists in the mind of the 
normal individual. 


The accidents of individual experience and mental imagery. 

Not only is the type of memory very different in different 
individuals, but the special contents differ according to the 
accidents of individual experience. Thus, if two persons 
have looked at the same scene from two different points of 
view, their imagery will be different ; certain near and vivid 
factors for one person will be vague and remote for the 
other. Then, too, individual attitudes react upon the con- 
tents of experience to determine the character of imagery. 
If an especially pleasing or disagreeable color has been pre- 
sented to a given individual, it may continue in his memory 
for a long time, while a second individual looking at the 
same color, but not greatly pleased or displeased by it, may 
very soon forget it altogether. 

Dependence on vividness and recency. In spite of indi- 
vidual differences in mental imagery, there are certain gen- 
eral statements which apply to all persons and all types of 
memory. All other conditions being equal, memory de- 
pends upon the vividness and recency of the sensory im- 
pression. It should be noticed that memory does not depend 
on intensity but on vividness. If intensity results in the con- 
centration of attention upon the impression, then intensity 
may indirectly help to fix the impression ; but a faint 
impression upon which attention has been centered will 
continue in memory long after the disappearance of an im- 
pression which passes without attention. The recency of an 
impression is also a matter of importance. Careful quanti- 
tative tests show that impressions fade with relative rapidity 
at first and at a very gradual rate later. We forget many 
impressions entirely in the first few moments after they are 
received. What we retain beyond the first brief period is 
more likely to continue as a relatively permanent addition 
to the content of consciousness. 

The training of memory. Much may be said with regard 
to the scope of memory and with regard to the possibility 


of increasing the scope of memory by training. It is doubt- 
less true that the ability to retain impressions differs greatly 
with different individuals ; some retaining many impressions 
and carrying them forward through long periods, others 
having little or no ability to retain. So clearly marked are 
these natural characteristics of different individuals that the 
changes produced through practice are relatively small. In- 
deed, Professor James asserts that there is no possibility of 
changing the degree of natural retentiveness through train- 
ing. This statement has been shown to be out of harmony 
with the facts, for there are evidences of increase in the 
scope of memory through training. Nevertheless, Pro- 
fessor James's statement is probably much nearer the truth 
than the popular assumption that memory can be radically 
changed through practice. 

Retention as distinguished from recall. Another general 
fact regarding memory is that experiences are not actively 
recalled without some present impression or related memory 
which serves as the motive or occasion for the exercise of 
memory. The mere retention of an impression is not the 
whole of memory. For example, at this moment there must 
be retained by every reader of these words hundreds of 
proper names. There is no motive for the recall of most 
of them. If one should find in the text, however, such a 
phrase as " author of the Iliad/' one of the proper names 
would be recalled and memory would become active for that 
one name. This name might in turn suggest other memories. 
The fact that memories are thus linked together and that 
active recall is always a matter of a train or sequence of 
processes was noticed long ago by Aristotle. He described 
the principles of memory, or, as they were later designated, 
the laws of association. There are two general principles 
of association which we may note : first, the principle of 
association by contiguity ; and, second, the principle of 
association by similarity or contrast. 



Association by contiguity. When one thinks of the letter 
A he is very likely to recall also the letter , because the 
two have so often followed each other in experience. The 
first line of a poem suggests the second ; the sight of one 
of two intimate friends suggests the other. In general, 
when two experiences have been intimately related in earlier 
experience, the appearance of one is likely to serve as a 
sufficient motive for the recall of the 

Association by similarity. When 
one sees a face which has eyes, or 
nose, or mouth like those of another 
person, the like feature is in many 
cases enough to recall the absent 
person. In such a case as this the 
two faces now associated need never 
have appeared together in the past ; 
it is enough that they contain the 
same feature. This relation between 
two experiences having a common 
factor is evidently a more complex 
fact than association by contiguity, 
for it involves a sufficient analysis 
or concentration of attention upon a 
single feature to separate it from its 
present surroundings and make it the link of connection with 
a group of experiences not now present. The diagram in 
Fig. 57 represents the situation. The circle A represents a 
single feature of the face now seen ; b, b, b are the other 
features. In a past experience, A has been part of a system 
of features of which c> c, c, were the others. If A becomes 
the subject of special attention, it can revive the elements 
c, c, c> and thus detach itself from b, b, b the features of 
the present complex in which it stands. In general, then, 
whenever a factor of experience now present has appeared 

FIG. 57. Association by 

The full-drawn circles repre- 
sent the elements of the pres- 
ent experience. Of these ele- 
ments A attaches itself also 
to the system of elements rep- 
resented by the dotted line 
circles. A, when taken with 
the circles b, b, fi, constitutes 
the present experience; '/, 
when taken with the circles 
f t <:, f, constitutes the recalled 
experience. A is obviously 
the center of relations be- 
tween the two systems 


in earlier experiences in a different combination, the earlier 
combination may be recalled through association by similarity. 

Association by contrast. Association by contrast will be 
clear after the foregoing discussion of association by simi- 
larity, for no contrast can exist without like elements. One 
may contrast a candle and the sun because they both give 
light, or the moon and a coin because they are both round, 
but in each of these cases the basis of the contrast is a 
common factor. 

New products evolved in ideation. Thus it is seen that 
memory images do not represent merely the traces of earlier 
experiences, but by continual association and readjustments 
memory images change their character and in the later 
stages show quite as much the effects of readjustments in 
mental life as the results of initial impression. When two 
ideas have been associated by contrast, there is an analysis 
which tends to break up the original memory images and 
bring to clear consciousness one element of the associated 
ideas together with what we may properly call the new idea 
of contrast. When the idea of contrast arises, the descrip- 
tive term " image " becomes less appropriate than it was 
for the simple ideas with which the discussion began. 

Ideas not all images. The idea of contrast is an idea of 
a higher type. It is very difficult to state what is the con- 
tent of such an idea. It is a kind of shock of difference, 
a feeling of intellectual opposition. Indeed, there are many 
psychologists who insist on the use of the term " imageless 
thought " in describing such an idea. They mean by this 
term to draw attention to the fact that the mind deals at 
these higher levels not with definite revivals of sensory con- 
tent but with certain tendencies of consciousness which are 
to be sharply distinguished from memory images. Perhaps 
the best description which can be given will be by the use 
of an analogy. The mind is calling up a series of images 
when suddenly it turns in a new direction. The abrupt 


turning is a real experience, often very vivid and important 
for all later thinking. Just at the moment of turning there 
must have been an experience. What was the experience 
of turning? It was an experience which linked together 
two images, but it was not in itself an image. 

Tendency to revert to imagery type. The more complex 
ideational experience becomes, the more elements there are 
which must thus be described as imageless. On the other 
hand, it is to be noted that there is a tendency to develop 
devices by which the mind can mark and hold steadily 
before it these imageless ideas. When one has had the 
experience of contrast, one tends to mark the experience 
by a word which will give it enough content to make it 
a stable unit in thought. 

Advantages of indirect forms of experience. All these 
statements draw attention to the fact that ideas are, more 
than any other phase of experience, flexible and subject to 
inner readjustment. Thus, even when dealing with revivals 
of perceptual experiences every person has his own peculiar 
image depending on his point of observation and his per- 
sonal powers of retention. Courts of law are familiar with 
this fact and attempt to eliminate by comparison of much 
testimony the purely personal elements which always attach 
to a memory image. 

The flexibility of ideas, as has already been pointed out, 
may be of great advantage because it puts the individual in 
possession of a device for thinking out changes in the per- 
ceptual world. When men put together ideas, they do so 
because ideas are flexible. If they get them put together 
in a productive way, they often make up a model to which 
later the hard material world may be made to conform. 

We are brought by this statement, as we have been sev- 
eral times before, to a recognition of the distinction between 
direct and indirect modes of adjustment to the world. The 
physiological conditions necessary to the formation of ideas 


are undoubtedly provided for in the nervous processes which 
go on in the association areas of the cerebrum. In the 
lower animals, where the association areas are small or 
lacking, there is little evidence of ideas. In these animals 
sensory processes pass to motor discharge with greater 
directness than in man. In like manner the infant seems 
to be wholly absorbed in percepts. This is related to the 
fact that the tracts in the association areas are the latest to 
develop, the process of development being, as noted in an 
earlier chapter, distinctly traceable for a period after birth. 
Animal behavior direct and perceptual, human behavior 
indirect and ideational. The significance of the evolution 
of the association areas can be seen by contrasting the 
modes of human behavior with the modes of behavior ex- 
hibited lower in the scale of life. If an animal is aroused 
to anger by some stimulation, it responds by directly attack- 
ing the source of the stimulation. If an animal is pleased 
by some form of agreeable excitation, it makes clear its 
pleasure in an immediate reaction. There is in animal life 
very little delay or indirection in response. When we con- 
trast all this with human life, we are impressed by the fact 
that man's activities are most of them indirect. They re- 
quire more time to mature. Thus, if a man sees an object 
passing before him, he may be thrown into a long train of 
thought rather than into a direct series of activities. The 
long train of thought is possible because man has a com- 
plex central nervous system through which the impression 
may circulate before it passes out as a motor impulse. Or 
man's action may be indirect in another sense, as was shown 
in the chapter on speech. Instead of attacking the object 
directly, he may call his neighbor and talk the matter over 
with him, ultimately arriving at a mode of action only after 
a long series of verbal preparations and plans which are 
indirect and related only in the most remote fashion to the 
object which yielded the original impression. 


The world of ideas comes ultimately to be a world of 
superior importance. Its laws of association are free and 
independent of the world of things. One can think of the 
cities of the country as belonging together because in the 
mind cities are associated, while in reality they are held 
apart by great stretches of territory. 

Influence of ideas on things. The result of the evolution 
of this inner world of ideas is that man ultimately puts 
together not only in his mind but in his actual conduct 
elements of the world which would never have been put 
together except for the laws of mental association. The 
laws of association are thus made to dominate the world 
of things. 

Tool-consciousness. Take, for example, the invention of 
tools. Primitive man was cut by a stone or torn by a 
thorn. Did he merely cry out with pain as an unintelli- 
gent animal might ? Not at all. He saw that the sharp 
edge which had injured him might be of great use to him 
if it could be brought into new relations. So he picked 
up the stone and plucked the thorn and put them to the 
uses which he saw first in his own mind and afterward 
realized in material readjustments. 

Knowledge of nervous process limited. It must be 
frankly admitted that this discussion has carried us beyond 
our knowledge of the conditions in the nervous system. 
We know in a general way what association areas are, 
but we do not know the details of their organization. We 
know ideas introspectively more intimately than we know 
their objective conditions. 

Traditionally, psychology has begun with ideas and given 
less attention to those lower and simpler forms of experi- 
ence with which we dealt in earlier chapters. For this 
reason the science of psychology has suffered in its rela- 
tions to the biological sciences. Either ideas have been 
thought of as facts wholly apart from bodily life or they 


have been declared in a vague way to be dependent on 
laws of physical being. Psychology has oscillated between 
a purely theoretical spiritualism and a crass materialism. 
The mind has been regarded either as wholly distinct or 
as part of the bodily phenomena. 

Consciousness as product of evolution. The view to which 
our study has led us can be expressed in evolutionary terms. 
Gradually the animal world, in working out its reactions to 
the environment, has evolved an inner world conditioned 
by indirect and tentative reactions. This inner world is 
social in many of its characteristics ; that is, it is a world 
through which individuals of the same type are drawn into 
sympathetic communication. The inner world is one in 
which ideas as substitutes for things are rearranged. The 
inner world is thus distinct from the lower levels of bodily 
adjustment, but is at the same time a part of the economy 
of individual relation to the world and is directly evolved 
out of the efforts at direct adjustment. 

Such an explanation of the place of consciousness in 
evolution gives us the fullest justification for our emphasis 
on those aspects of ideas which are not copies or reproduc- 
tions of sensory impressions but new modes of rearranging 

We shall continue our discussion, accordingly, with a 
treatment of the changes produced in experience through 
the most elaborate rearrangements in ideas. 



Adaptation through ideas. The animal adapts itself to 
its environment by cultivating better modes of direct reac- 
tion, such as greater speed of running or greater skill in 
the use of its teeth or claws. Gradually there appears 
in the highest animals a new mode of adjustment in the 
tendency to organize into social groups. The social group 
is a protective device which gives the individual greater 
strength than he can cultivate in his own individual organ- 
ism. As soon as the social group evolves there must grow 
up, and there do grow up, types of activity designed to 
hold the group together. In man this latter phase of evo- 
lution culminates, and social cooperation becomes one of the 
dominant facts in life. No longer does man compete with 
his enemies by cultivating greater and stronger muscles ; 
he meets the struggle for existence by social cooperation. 
His reactions on the world are in large measure indirect. 
He invents a world of social forms which can be described 
only by saying that it is an artificial environment of human 

In a very real sense this means the evolution of a new 
type of adaptation. The competitions of human life are at 
a new level, wholly different from those of animal life. 
The character of this new type of adaptation can be studied 
through an analysis of one system of human behavior such 
as commerce, which has no parallel whatsoever in the 
animal world. 



Early stages of barter. In the earliest stages of exchange 
the parties to the transaction demanded direct contact with 
the objects bartered. Even at this primitive stage much 
self-control and much regard for social relations are ex- 
hibited. The fact that men will barter at all proves that 
they have cultivated ideas to the extent of refraining from 
mere brutal seizure of that which they desire and to the 
extent of realizing the possibility of giving up one thing 
for another. Barter involves in its crudest form some 
powers of 'thought and some attention to social relations. 
But barter is always perceptual in its demand that the 
commodities to be exchanged be directly accessible in 
tangible and visible form. 

Barter perceptual. The stories of primitive barter which 
show the savage duped by the gaudy color of cheap wares 
bear eloquent testimony to the fact that perception is at 
this early stage not yet replaced by ideas. 

Standard values. After barter began to be understood 
and widely practiced, there was cultivated a desire for uni- 
formity ; that is, for standard methods of exchange. Some 
commodity more durable in its qualities than the rest began 
to serve as a common standard to which all transactions 
were referred. Among hunting tribes all barter is standard- 
ized in terms of furs. In grazing communities sheep and 
cattle become the standards. Through the use of such 
standards, ideas of uniform value were developed, and the 
mere showy perceptual characteristics of objects receded 
into the background. 

Symbolic values. The next step in exchange comes 
when some very permanent commodity takes on symbolic 
value. Wampum is prized not alone because it is a beau- 
tiful string of shells but because it serves as a counter and 
may be passed around as a promissory note for future 
delivery of a stipulated number of pelts or tents or arrows. 
By the time this stage is reached we must assume high 


powers of association. Wampum has value now because 
it calls up ideas and because the social group in increasing 
measure guarantees the ideas connected with the symbol. 

As with wampum, so with the metals. The ideational 
values are finally marked on the metal. Then comes the 
paper substitute for the metal and finally the various forms 
of commercial credit of modern commerce. One has only 
to represent to himself the scene which would follow if a 
bank note were offered to a savage hunter in exchange for 
game to realize how far from direct perceptual experience 
modern commerce has gone. 

Evolution from perception to ideas. This sketch of the 
evolution of barter into commercial exchange could be par- 
alleled in every field of human action. Manufacturing with 
machinery has replaced the simpler direct contacts of primi- 
tive life. Travel by borrowed power of animals and finally 
by mechanical forces has largely replaced migration of the 
savage type. Sanitary regulations and settled modes of urban 
life have replaced the life of the forest and the wilderness. 

How has all this evolution come about ? There is one and 
only one answer. Man has learned to combine and recom- 
bine ideas, to call on his neighbor for cooperation and for 
the further comparison of ideas, and to meet the needs of 
life indirectly rather than by direct perceptual responses. 

Higher controls of conduct. The transformation of life 
thus outlined has not gone on without bringing about the 
most radical internal changes in the mind of man. To 
the direct and vivid emotions which accompany instinctive 
reaction have been added trains of ideas which lead to 
deliberate forms of behavior. Human nature has become 
complex. There is an element of animal life and of primi- 
tive devotion to perceptions in every man. We shall never 
outgrow instincts or our native impulses to seize the things 
about us. But above and beyond these direct modes of 
adaptation there is the higher world of ideas. In dealing 


with this higher world a new type of experience has been 
evolved. There are new pleasures which come from the fit- 
ting together of ideas. There are new forms of displeasure 
which come from the clash of ideas. 

Ideational attitudes. For example, there is a shock when 
one hears a profane word which is little less than the shock 
from a physical blow. The name of the Deity has associated 
itself in all experience with the attitude of reverence, and 
when this name is taken out of its proper associations and 
used in a reckless fashion, the emotional recoil is violent. 

Other examples can be drawn from the cultivated demands 
for the use of proper grammatical forms. The child gradu- 
ally learns that a plural noun demands a plural verb. The 
shock which comes from hearing a violation of this rule is 
quite as unpleasant as the shock from a sharp, cold breeze 
striking the skin. Furthermore, the inner muscular recoils 
in the two cases are not unlike. Both involve, among other 
factors, an interruption of respiration and a change in the 
rate of the heartbeat. 

Ideas as substitutes for impressions. When we speak of 
the world of ideas as a real world, all the foregoing con- 
siderations must be kept in mind. Ideas are real in prompting 
behavior and in giving directions to our acts. Ideas may 
be followed by habitual reactions until they come to demand 
these reactions quite as much as do things seen through 
the eye or heard through the ear. Ideas may influence the 
train of attention quite as much as percepts. For example, 
the man who is lost in thought does not attend to the ob- 
ject coming toward his eyes. In short, ideas have values 
comparable in all respects to percepts and in some respects 
quite superior. 

Imagination as reorganization of ideas. In this chapter 
we shall discuss some of the changes which take place in 
this world of ideas, for it is important if we are to under- 
stand the world in which man lives that we shall know the 


laws of change in his world of ideas. In an earlier connec- 
tion the laws of memory were discussed. It was there 
shown that in some measure the mind holds its ideas fixed 
and brings them back under proper conditions so that past 
experiences may operate in present surroundings. When 
ideas are thus carried forward, they are called memories in 
the strict sense, or sometimes they are called images. It 
was pointed out in that earlier treatment of the matter that 
memories undergo a change in experience. We now turn 
to the more elaborate types of such change. For these 
types of change there are a number of names. Sometimes 
ideas are described as imaginations. This term is used to 
indicate that a mere rearrangement of elements of memories 
has been made. One imagines a horse with wings. The 
source of the idea " horse " is memory, likewise of the idea 
"' wings/' but the union of these two sets of ideas is an act 
of the imagination. When the combinations which go on 
in consciousness are purely capricious, we speak of fanciful 
imaginations. When, on the other hand, recombinations of 
mental processes are worked out systematically and coher- 
ently, we speak of scientific imagination. Thus a dragon is a 
fancy ; the imagination of a Columbus or a Watt is scientific 
and constructive. 

Personifying imagination. One of the most primitive 
forms of imagination is that exhibited by savages when 
they attribute to inanimate objects the personal character- 
istics which they find in themselves. The savage never 
thinks of thunder or of the wind without putting back of it 
in his imagination some personal agency. This form of con- 
structive thought is the simplest which could originate in 
a personal consciousness. An emotion of anger is a more 
direct explanation for a natural catastrophe than is some 
abstract statement referring to physical force. To modern 
thought the myths of early peoples seem like the play of 
the most capricious imagination ; to the mind untrained in 


the forms of critical scientific imagination nothing could 
be more natural than a myth. Even the trained mind 
derives pleasure from the personification of objects, because 
it is easy to use the factors from personal experience in all 
manner of combinations. 

Imaginations occasions of useless activities. Early man 
was led by his imaginations to undertake many useless 
forms of activity. Thus, he attempted to propitiate the 
personalities which his own mind had put into streams and 
mountains and trees. There was no direct evidence that 
his imaginations were not in conformity with the facts, and 
hence the imaginations went on increasing in complexity 
until they broke down by their own incoherency. 

Critical tests of imaginations. This reference to the fanci- 
ful imaginations of primitive man introduces us to the 
discussion of the more productive forms of imagination in 
which the mind does not weave together factors of expert 
ence capriciously, but under the guidance of conditions 
which limit the freedom of the constructive process. When 
imagination is used for purposes of practical construction, 
or for the later purposes of science, its products must be 
subjected to critical examination by the individual who 
develops them. A first principle of criticism of imagination 
may be described as the principle of empirical test through 
application. The constructs of imagination may be used to 
guide activities, and if the activities are not successful, it 
will obviously be necessary to go over again the combinations 
which were worked out in consciousness and to revise these 
combinations with a view to making them more suitable 
bases for action. We may speak of this form of criticism 
as the practical or empirical test of imagination. If, for 
example, a given individual finds that he must get across 
a certain stream, he is likely, if he has time and the neces- 
sary mental development, to consider first in imagination 
the means by which he can get across. He determines in 


thought that it would be possible by bringing together 
certain appliances to make the passage easy. - If, on trying 
the expedients which have suggested themselves in his 
thought process, he finds that the idea is a good one, 
his imagination receives the confirmation which comes from 
practical utility. If, on the other hand, his imagined device 
breaks down when put to the practical test, he will be led 
to further considerations of a more elaborate character, in 
order to correct the deficiences which have been shown by 
the practical test to exist in his imagination. 

Empirical test often inapplicable. There are many ideal 
constructions which cannot be subjected directly to practical 
tests. For example, in the course of human history man has 
constantly been trying to reconstruct in imagination the process 
of the development of the earth on which he lives. Our modern 
Science of geology is an elaborate effort to reconstruct the 
history of the earth. Obviously, the ideas reached by geology 
cannot be tested by any single practical act. Man has de- 
veloped, accordingly, a system of criteria by which he tests 
the validity of his ideal constructions, even when these ideal 
constructions are not directly intended for the practical uses 
of life. These theoretical criteria, as we may call them, can 
be shown to grow out of the nature of experience itself. 

The test of internal agreement. It is demanded by every 
human consciousness that the elements of any given idea 
shall be harmonious. We have seen that it is true of per- 
ceptual processes that they have unity and arrangement, such 
that all of the conflicting qualitative factors are provided for 
in a single experience through the arrangement of the ele- 
ments of experience in spatial and temporal series. Thus, 
even in perceptual consciousness, a certain coherency and 
harmony are required of the elements before they can enter 
into the percept. Still more when we come to the constructs 
of imagination is there a demand for harmony of relations 
among the factors which are presented. Thus it would be 


difficult to think of one physical substance as subject to gravity 
and another as not. If any factor or relation is recognizably 
incongruous with the system of experiences into which it is 
introduced, then that system of experience will have to be 
rearranged until the whole organization is adapted to the re- 
ception of the element which was out of harmony with the 
other elements, or else the incongruous element will have to 
be rejected. Thus, if all substances fall toward the earth and 
smoke rises, we must devise an explanation. Scientific imagi- 
nation, when not susceptible to practical tests, is thus nothing 
more nor less than the effort to develop an elaborate system 
of congruous ideas. 

The criterion of coherency a product of development. 
Primitive man does not have this criterion of the harmony 
of all of the elements of thought as fully developed as 
does modern science. This is in part due to the limitations 
of primitive experience : as when a savage believes thunder 
to be a voice because he knows little of either the thunder 
or of the mechanism which produces the voice. It is in 
part due to a general uncritical attitude : as when in Greek 
mythology the earth is borne upon the shoulders of Atlas 
because attention was not ordinarily concentrated on the 
necessity of supporting Atlas. 

The demand for coherency as exhibited in constructive 
scientific ideas. It cannot be asserted that the criterion of 
harmony among the elements of imagination is applied with 
full success even in modern science, but examples can be 
given without limit of its application. Thus, it is quite im- 
possible for us to think of the earth and the sun as related 
to each other without, at the same time, conceiving of some 
kind of bridge between the earth and the sun. Science has 
therefore developed the notion of the ether as a continuous 
substance between the earth and all other points in the uni- 
verse. The ether is not a factor of direct experience in any 
form. It is demanded in scientific considerations in order to 


make the idea of the solar system and of the universe a co- 
herent thinkable idea. Ether may, accordingly, be called a 
product of imagination. This statement does not deal with 
the question of its objective reality ; it merely asserts that 
ether comes into scientific experience in response to a demand 
for harmony in the ideational system, not through perception. 
Uncritical imaginations. The extent to which imaginations 
are criticized depends upon the development of the individ- 
ual who possesses them and upon the type of ideas under 
examination. A good illustration of the dependence of criti- 
cism on \pdividual development was given above in discuss- 
ing the myths of primitive peoples. Another may be found 
in the imaginations of children. It has frequently been said 
that children are more imaginative than adults. This state- 
ment is based on the observation that a child will imagine 
many things in connection with its toys and derive a great 
deal of satisfaction from these imaginations, when an adult 
would be so clearly conscious of the falsity of the imagina- 
tions that he would derive little pleasure from them. This 
observation does not show that the child is more imaginative 
than the adult, but it shows that the imaginations in early life 
are not subjected to any careful criticism. Almost any men- 
tal combination is accepted by the child and enjoyed for the 
moment without serious criticism. Indeed, the child's experi- 
ence is often like the savage's, too meager to make it possi- 
ble for him to construct any systems of thought that shall 
constitute the basis for the criticism of his particular imagi- 
nation. Furthermore, many of the child's activities are not 
sufficiently serious to constitute practical tests for his imagi- 
native constructs. As life goes on and the systems of thought 
become more and more closely united with each other, and 
the practical demands of individual existence come to be 
more strenuous, the indulgence in fanciful imaginations un- 
checked by criticism becomes less common than it was in 
early childhood. 


Literary imagination and the canon of coherency. An illus- 
tration of the way in which the products of imagination may 
be subjected to different kinds of criticism is to be found in 
the case of literary forms. Literature is an effort to construct 
through the exercise of imagination a system of thought 
which deals with human interests and human activities. If 
this constructive process purports to be held closely in agree- 
ment with certain records, we call it historical in character, 
and we demand that it shall conform to the canons of con- 
gruity with all the legitimate records of the period in question. 
If the construction is, on the other hand, confessedly free 
from any particular reference to definite situations, we call it 
imaginative literature and recognize its product as fiction. 
Even in this case we demand of literature that it shall have 
relation to experience. A wholly unnatural creation has no 
justification, even in fiction. The particular circumstances 
which are grouped together may be circumstances which 
never were brought together in the course of human history 
or individual life, but the principles of combination must 
be recognizable as principles in harmony with the general 
nature of human experience. 

The canons of criticism in literature are by no means as 
clearly definable as are the canons of criticism in scientific 
thought. The reason for this is that literature includes wide 
variations in types of individual experience and consequently 
permits laxness in the demand that the imagined experiences 
shall conform to the particular type of any individual's life. 
It is not difficult for us to accept certain rather grotesque and 
unusual combinations, provided these combinations of experi- 
ence are referred to periods in time or points in space remote 
from those with which we are ordinarily in contact. 

The uncritical forms of thought which preceded science. 
The beginnings of what we call scientific thought are obscure, 
because the careful comparison of scientific ideas is preceded, 
at times by much practical adjustment of activity to the 


environment and, at other times, by much uncritical specula- 
tion. The practical effort to adjust one's activities to the 
world leads to certain systems of ideas. Thus, the child 
always looks for the causes of the happenings which come 
into his experience long before he formulates in clear, explicit 
thought the statement that every event has a cause. When 
he hears a noise, he has a vague notion of something back of 
the noise. In the same way men must have sought causes in 
practical life long before there was any science. They also 
had ideas which they used in the constructive activities of 
life, such as ideas regarding the strength and durability of 
certain building materials. In addition to these practical 
ideas there were speculative ideas. Superstitions of all kinds 
flourished in the uncritical thought of primitive man. If a 
bird flew across his path, he thought of infinite varieties of 
good or ill. There is a certain sense in which all these 
superstitious and practical ideas constitute the beginnings 
of science. They furnished the thought material which, 
when sifted and organized into systematic form, constitutes 
science. The methods for sifting and organizing this thought 
material are the essential additions to mental life which came 
with science. 

First sciences limited to facts remote from life. When 
the systems of coherent ideas began to emerge from the 
original chaos of practical and superstitious constructs, it is 
striking that the facts remote from individual control were 
the earliest to yield to the organizing endeavors of thought. 
It was possible to construct a system of consistent scientific 
ideas regarding celestial movements, because these remoter 
facts were far enough from individual life to be observed 
without perplexing minor incongruities. The nearer facts of 
any situation are too full of variations to fall into anything 
like an harmonious system without the most elaborate idea- 
tional reconstruction. Thus, a science of social relations and 
a science of mental processes could develop only after man 


had become so thoroughly devoted to the forms of scientific 
thought that he could follow facts in long series, could 
deliberately assume some attitude other than that of direct 
personal relationship, and, consequently, could trace out 
certain abstract relations in the midst of the complex of 
varying elements. 

Scientific concepts. Let us consider one of the scientific 
constructs built up in the course of the development of phys- 
ical science. Such a construct is called a scientific concept. 
An example of such a concept is that of the atom. Man 
found, as he examined the bodies about him, that these 
bodies underwent certain changes which were indicative of 
unperceived characteristics. It was important to understand 
these characteristics in dealing with the bodies for practical 
purposes. For example, water freezes, stones crumble, metals 
expand and contract with changes in temperature. Man must 
have noted many of these changes and many of their condi- 
tions very early in his dealings with such substances, but he 
had no direct means of observing what went on in the mass 
of the matter itself. He therefore set about, at least as far 
back as the early Greeks, trying to form some idea of the 
changes which must take place within the substance, in order 
to explain the changes which he observed. Certain of the 
Greek thinkers drew upon the forms of experience with 
which they were familiar namely, their experience of com- 
posite matter made of separate parts and formulated the 
concept that all substances are made up of particles which 
are separated by intervals of space. They concluded, further, 
that the particles which they assumed as the elements of the 
substance must be capable of greater and less separation 
from one another, as in expansion and contraction, and also 
that they must be capable of rearrangements, such that the 
appearance of the whole substance is modified without de- 
stroying the particles. Through such considerations as these, 
some of the early scientists came ultimately to refer to the 


smallest particles of any given substance as atoms, and to 
describe these atoms as separated from one another by space, 
and as constituting by their composition the observed body. 
The physicist or chemist to-day uses this very valuable con- 
cept in his thought about substances ; he constantly refers 
to atoms, although he never expects that he will be able to 
see an atom, or to test the validity of his mental construct 
by the sense of touch. Indeed, the atom is an idea needed 
by science just because science has to bring together into 
an harmonious ideal system more than can be discovered in 
any single inspection or handling of an object. 

Validity of concepts. When such statements as these are 
made, some persons think that the validity of the scientific 
concept is seriously called in question. On the contrary, 
there is no higher guarantee for any form of knowledge 
than that it is demanded in order to render congruous the 
whole system of experience. As we have seen, in all of the 
earlier discussions of perception and ideation, experience has 
many higher phases which cannot be resolved into direct 
sensory elements. The validity of space as a form of ex- 
perience cannot be called in question because it is a relational 
rather than a sensational phase of experience. For similar 
reasons, the construction of a concept is justified as a result 
of a higher organization of experience. The method of arriv- 
ing at such an ideal construct is indeed indirect; but the 
concept has all of the validity which belongs to experience 
as an organized system. 

Abstraction. When ideas are completely under the con- 
trol of the individual, they may be arranged according to 
principles which are set up by thought itself. Thus, one 
may decide that it is desirable to group together all round 
objects, or all hollow objects. There then arises an idea of 
roundness or of hollowness which is called an abstract idea. 
The term " abstract " means that something has been " cut 
off." When we think of roundness alone, we neglect color 


and position and weight. We can cut off the one quality 
and make it a subject of attention because the power of 
thought has been developed to the point where inner motives 
are stronger than external motives. 

Generalization. Furthermore, whenever the mind reaches 
the stage where it can select and concentrate on single as- 
pects or attributes of experience, it can at the same time 
group together under each selected attribute many individual 
cases. This is called the power of generalization. Thus, 
once the mind has fixed on roundness as a selected attribute 
of objects, it can bring together and group in one class the 
earth, a ball, an apple, etc. 

Abstraction and generalization are valuable not merely as 
feats of inner control ; they make possible highly developed 
forms of conduct. If one can select and hold steadily be- 
fore the mind one aspect of an object, conduct can be made 
more effective through concentration than when the observer 
is distracted and confused by an effort to deal with tinanalyzed 

We shall find ourselves coming back to this topic later 
when we take up volition as the highest form of behavior. 
The more fully ideas are abstracted and generalized, the 
more conduct will be guided by inner motives. The man 
who sees values in objects and decides to be thrifty is guided 
by an abstraction and is so far forth acting in response to 
an inner motive. 

Judgments and reasoning. After a concept has been for- 
mulated, it may become part of a still more complex mental 
process which includes several ideas. Thus, when two con- 
cepts are related as in the statement " The sun is the center 
of the solar system/' the whole process is termed a judgment. 
When two or more judgments are united for the purpose 
of setting up an even more complex combination, the whole 
process is called reasoning. An example of reasoning is as 
jfollows: The sun is the center of the solar system; any 


central body in a system of this type must have a control- 
ling influence over the other members of the system ; hence 
we should look for the control of the sun over the earth and 
the other planets. 

Logic. It is not in place here to give an account of the 
various types of judgment and reasoning. It is the function 
of the science of logic to study the complex processes of 
thought and to develop the rules under which the validity 
of these processes may be tested. We must content our- 
selves in an * introductory treatment such as this with certain 
comments which will serve to call attention to the psycho- 
logical character of these complex forms of ideational experi- 
ence. Perhaps the best single topic with which to introduce 
a psychology of logic is the topic of belief. Let us consider, 
therefore, what is meant by the statement " I believe a 
certain conclusion to be true." 

Primitive belief. The first and most direct case of belief 
is that in which I assent to any combination of ideas be- 
cause my natural tendency is to accept combinations of ideas 
when there is no reason to deny what is presented. The 
psychological fact is that ideas which stand together in the 
mind unchallenged by other experiences are accepted as 
coherent and acceptable. Thus, when I was a child I be- 
lieved in Jack the Giant Killer and Jack and the Bean Stalk 
because my experience was too limited to deny these stories. 

Belief after hesitation. A higher form of belief comes 
after one has hesitated. In such cases the statements are 
not immediately accepted. This means that they arouse 
series of associations which suggest various conflicting forms 
of statement. At this stage there is a restlessness, and other 
forms of statement are tried ; other authorities are cited. It 
may be that one goes out and tests the conclusion by practi- 
cal behavior. If the first opposition is broken down by one 
or the other of these influences, there results in the end a 
waning of the suggested contradictions. 


Belief a positive psychological fact. There can be no 
doubt that belief in all these cases is something more than 
the mere hearing of certain sounds or the mere coupling 
together of certain ideas. When we say that the idea is 
accepted, we undoubtedly refer to some positive physiolog- 
ical process. Belief is related to the fact that a sensory 
impression goes through the nervous system to some form 
of positive expression without being opposed. If it were 
checked by encountering some current opposing it, we 
should be restless and the feeling would be one of hesita- 
tion. Assent is a genuine process of a positive type. Such 
a positive process will usually issue in a definite motor re- 
sponse. It may be that the motor process is a mere nod 
of the head or an inner emotional twinge. The important 
fact is that the nervous process issues in a positive dis- 
charge. The motor discharge may be in itself insignificant, 
but the fact that it occurs and the fact that it is positive 
in character give to experience that special turn or coloring 
which we designate by the term " belief." 

Spurious verbal belief. Such considerations lead to brief 
comment on what is called mere verbal assent. It is possi- 
ble for one to give assent carelessly by merely repeating 
what he hears. Many students accept what they find in 
books in this way. The motor paths leading to the speech 
centers seem to be stimulated directly by the eyes as they 
read, or by the ears as they hear. Reaction is of little value 
in such cases. It is a kind of shunt circuit. The impres- 
sion does not get mixed in the association areas with any 
forms of ideation which confuse or interrupt the direct 
transmission to the speech center. The result is a specious 
belief and a useless form of nervous and mental reaction. 
There is nothing more fatal to true mental organization 
than this short-circuiting of the eyes and ears to the vocal 
centers. It is one of the penalties which man pays for the 
development of an indirect mode of behavior. 


Habitual belief. Another highly developed form of belief 
is that which comes from the organization in individual life 
of certain habitual modes of response. Thus the physicist 
learns, in spite of sensory testimony to the contrary, to 
think of every substance as porous. He finds that his be- 
liefs are all conditioned by conformity to this cultivated 
idea. If any remark is made or any fact turns up which 
runs counter to this accepted principle, the new proposal 
will be rejected. Beliefs are thus not unlike the funda- 
mental emotional attitudes. They are very real factors in 
thought, though they are not made up of memory images. 

Religious belief not instinctive. Certain writers, im- 
pressed with the similarity of beliefs to emotional attitudes, 
have regarded certain well-established beliefs, such as reli- 
gious beliefs, as instinctive. The belief in the Deity, in im- 
mortality, in the certainty of moral categories, is held by 
these authors to be no less primitive in human nature than 
the fundamental desire for food, for physical comfort, and for 
companionship. On the other hand, it is held by others that 
such beliefs are the results of developed systems of ideas. 

Sentiments not instinctive. The latter formula, which is 
the more defensible, suggests the explanation of many of 
the so-called sentiments and tastes of later life. They are 
connected with acquired modes of behavior. Certainly, if 
one studies the life and practices of savages, he finds a 
striking parallelism between behavior and tribal belief. The 
savage practices certain customs, and they come to have for 
him the sanction of the highest religious demands. So in 
civilized life as well. The sanctions of society are bred into 
our very beings until we believe in the necessity of social 

Social life and the higher mental processes. Efforts have 
been made in the recent literature of sociology and psychol- 
ogy to explain social institutions as the products of instinc- 
tive tendencies. The argument of this chapter is that belief 


which grows out of systematic thinking, while it may have 
the appearance of an instinctive emotion, is in reality the 
product of the highest types of mental activity. Social 
sanctions are evolved through association and comparisons 
of ideas and through the evolution of modes of social be- 
havior. Society may rest on instinctive tendencies, but its 
forms and operations are all worked out through the use of 
language. Everywhere in social life one finds abstractions, 
now of a higher type, now of a lower. Social life is a prod- 
uct of thought and ideation, not of blind instinct. 

Fields for the application of psychology of ideas. This 
chapter must close with these mere outlines of discussions 
of the higher mental life. That there is a field for a psy- 
chological study of all the higher forms of appreciation is 
indicated by what has been said. This matter will be 
touched on again in a later chapter dealing with the appli- 
cations of psychology. 

There is a psychology of invention in which the indi 
vidual is studied at those critical moments when a new set 
of associations is being evolved within him. There is a 
psychology of education which must distinguish between 
learning of a true type and learning to repeat words out of 
books. There is a psychology of social theory and social 
conduct. The formula for all of these is a formula of organ- 
ized mental processes leading to various forms of expres- 
sion. If the student has grasped the import of this general 
formula, he will be able to unravel the particular types of 
organization which appear in each of these spheres. 



The idea of self sometimes regarded as matter of direct 
knowledge. ^ Among the ideas which are built up in practical 
life and refined by scientific study, there is one which is of 
special significance to the student of psychology. It is the 
idea which each person has of himself. So significant is 
this idea for our ordinary thought that it has sometimes 
been described in terms which imply that one knows one- 
self directly as though through some kind of immediate per^ 
ception. One is supposed to look within and there find an 
inner reality which is known and recognized without any of 
the ordinary steps that enter into the process of knowing 

Idea of self a concept. That the self is a being which 
can be directly perceived is, however, contradicted by all the 
facts of development. The child does not know himself 
until after he has had a series of experiences. Even the 
adult has something to learn about himself with each new 
turn of conscious life. The idea of self must therefore be 
described as a concept which matures in the course of ex- 
perience just as does any other scientific or practical idea. 

First stages of personal development not self-conscious. 
Let us attempt to formulate what we know of the most 
primitive stages of experience, in order that we may arrive 
at some notion of what consciousness is like before there is 
any recognition of the self. The simplest forms of animal 
behavior, as has been repeatedly pointed out, do not indicate 
any clear marking off of impression from expression. The 



activity which follows upon impression is so direct that there 
is no time for the interpolation of any factor, either in the 
nervous system or in consciousness, between impression and 
expression. Much the same kind of situation appears when 
we examine the human infant. There is an inherited mech- 
anism in the instincts which supplies appropriate responses 
to stimuli, and as a result there is little or no consciousness 
of any kind involved in reacting to the impression cer- 
tainly no recognition of one's own personality. Sensation 
and response blend in an experience which is overwhelm- 
ingly emotional in character and not at all capable of dis- 
tinguishing one factor of the situation from another. Such 
experience includes no separate idea of oneself. 

Gradual discrimination of self from things. The develop- 
ment from this point is toward the discrimination of phases 
of experience. Probably there is a gradual differentiation of 
the sensory' elements from one another and of the sensory 
elements from the individual's attitudes and responses. As 
soon as things begin to be recognized, there must be a 
tendency to formulate all one's feelings and attitudes into 
a kind of personal unity or self. The construction of such 
a personal core or self in contrast with things is a slow and 
complex process. 

Child's early notion of self largely objective. Undoubt- 
edly, a child's contact with his own body is very important 
in building up some early crude distinctions between im- 
pressions and attitudes. When the child handles his own 
feet, he finds that the impression he receives, and the atti- 
tudes into which he is thrown by the double stimulation of 
two parts of his body, are entirely different from the impres- 
sions which he receives and the simpler attitudes into which 
he is thrown by the stimulation of one of his members 
through some external object. He thus comes to distinguish 
between his body and the external world. The body is a 
part of the world with characteristics different from the 


other factors which he recognizes through his senses. There 
is probably some ground in this fact for the statement that 
the child's earliest recognition of himself is of the nature of 
a percept and relates to his physical organism. The rela- 
tively objective character of the experience of self at this 
stage is shown by the fact that, in addition to his own body, 
the child attaches to himself, as a part of what he calls him- 
self, the possessions which he comes to recognize as his 
individual property. The external world is broken up into the 
meum and tniim, and the general notion of that which belongs 
to the individual himself is gradually distinguished from that 
which belongs to others, but the meum is not primarily a sub- 
jective fact. It is looked at through consciousness, but that 
consciousness is very little self-consciousness in the purely 
subjective sense in which we use that term in mature life. 

The idea of self as related to discrimination between the 
objective and subjective. Such considerations as these tend 
to show that the idea of self is a product of discrimina- 
tive analysis rather than a fact of immediate perceptual 
consciousness. So far as we understand immediate con- 
sciousness in its early stages, there appears to be little or 
no ground for assuming that there is present any complete 
discrimination of the self on the one hand and things on 
the other. Even in mature life the distinction between the 
self and nonself is not always drawn. The man who is 
hurrying to catch a street car has a vivid experience, but 
it is not nicely analyzed. The hungry man with food before 
him is little more self-conscious, if, indeed, any more self- 
conscious, than the animal which spends all of its time and 
energy in the eager pursuit of food. 

The self discovered by contrast with not-self. What 
brings any individual to a clear recognition of himself will 
probably depend upon the accidents of individual fortune. 
The struggle of personal interests with some unyielding 
objective fact may accomplish it. The development of an 


idea of some other self, opposed in interest to the self, is 
often a powerful incentive to the recognition of one's own 
self. Historically, it has repeatedly been pointed out that 
the national spirit, which is analogous to personal self- 
consciousness, often grows out of some contest. In like 
fashion, the clear idea of the self undoubtedly rises out of 
some contest of opposing interests. 

Social consciousness and self-consciousness. The conflict 
of interests may take a purely social form, as in the use of 
language. One sees that all the words referring to spatial 
directions, for example, center about one's own body. One 
finds that active or passive verbs have reference to some 
person. One finds, in short, that one's own expressions are 
arranged and organized around a different center than are 
the expressions of every other human being. So impressive 
does this contrast between individual attitudes become that 
ultimately, when we find ourselves in agreement with others, 
we are impressed with the agreement, as in earlier cases we 
were impressed by the differences, in mental attitude. The 
result is that our contact with the social world is a constant 
stimulus to the development of a more and more clearly 
defined recognition of the self. The child undoubtedly 
comes to self-consciousness through his use of language 
more than through any other means. 

The self at first not a scientific concept, but a practical 
concept. Some idea of the self, based upon discrimination 
of one's own attitudes from the attitudes of other persons, 
is developed in a wholly unscientific way by every individual, 
just as the discrimination of the individual body and of 
one's personal possessions from the rest of the physical 
world arises naturally in the course of personal life without 
any effort at systematic definition. Beyond this natural dis- 
crimination one may attempt to cultivate a more highly 
refined formulation of his personal attitudes and personal 
characteristics, and yet not pass directly into science. 


Cultivated self-consciousness. To illustrate certain cases 
in which self-consciousness takes a form other than the 
scientific, we may refer first to literary criticism. If a 
reader begins the criticism of any piece of literature, he 
will constantly be contrasting the impression which tl\e 
author intended to produce with the personal attitude 
aroused in himself through the statements which he reads. 
There will thus be a certain social contrast between the 
individual and the author, and this is deliberately cultivated 
for the purpose of refining and critically elaborating one's 
own taste. In some cases this may take the form of an 
effort to conform personal tastes or attitudes to the stand- 
ards which have evidently been adopted by great masters. 
There is here an unquestionable tendency to refine self- 
consciousness at the same time that one cultivates attitudes 
toward the objective facts. 

The religious motive for self -consciousness. Another 
illustration of the nonscientific cultivation of the concept 
of the self will appear if we refer to the attitude which is 
assumed by many individuals in the contemplation of their 
awn origin and destiny. The religious attitude has un- 
doubtedly contributed more to the definition of self in the 
minds of unscientific individuals than any other system of 
thought or activity in the world's history. One here asks 
himself how fully his own personal attitudes conform to 
what he understands to be the demands of the laws gov- 
erning his destiny. The system of laws, which he accepts 
as a system of higher law, may be derived from very dif- 
ferent sources ; but in any case, whether it be the religious 
faith of the savage or the systematized theology of the 
most highly cultivated devotee of an elaborate religious 
system, there is always in religious thought and aspiration a 
comparison between the demands of the religious system and 
the demands of individual interest and feeling. The notion 
of the self comes to have a compactness and importance 


under this system of religious self-examination which it 
could never attain by mere social contrast with the experi- 
ences of other individuals or in the presence of physical 
objects. Questions of ultimate destiny arise, and these 
are answered in terms of a self which is much more 
highly elaborated than the bodily or material self upon 
which man concentrates his attention in the early stages 
of individual life or the primitive stages of mental develop- 
ment. We find, however, many indications, as we look 
into savage customs, of a curious mixture of the primitive 
bodily self and the religious self. The savage always pro- 
tects with great care the bodily remains of those whom he 
would serve, and he mutilates and destroys the body of an 
enemy. The bodily self is here recognized as the tangible 
aspect of personality. 

Scientific idea of personality. As contrasted with these 
unsystematic efforts at self-realization, the science of psy- 
chology aims to build up a thorough idea of the nature 
and relations of the self. The self becomes for our science 
a being whose laws of organized life must be discovered 
and explained. 

The self can be fully described and understood only 
through studies of the type which have been outlined in 
the foregoing chapters. The self is a being which per- 
ceives and forms concepts ; it remembers and expresses 
itself in regular habits. It is characterized by emotions 
and by elaborate ideational forms of thought. The self is, 
however, not merely a chance collection of percepts and 
habits and ideas. There is one attribute of the conscious 
self which stands out as of paramount importance. The 
self is a unity. It expresses itself now in one direction, 
now in another, but in all its various manifestations it is 
an organized unit. Whatever conscious states the self pos- 
sesses are modified by virtue of the fact that all aspects 
of individual consciousness are united in the one being. 


The only analogy which can be used in expounding this 
type of being is the analogy of life. The living being is 
an organized unity, 

The chief item in the concept of life the abstract idea 
of organization. Such statements as the foregoing are con- 
fusing to certain students of science. They profess to 
know what an atom or an object is, but they say of life 
that it is not a scientific entity because it is not simple, 
and they say of conscious selves that they are not entities 
in any such scientific sense as are atoms and physical 
forces. Some chemists, for example, would reduce life to 
mere coexistence of atoms in a complex molecule of pro- 
toplasm. It is, indeed, true that there is a chemistry of 
protoplasm. The significant fact, however, is that once 
the molecule of protoplasm became organized it began to 
exercise functions which were absolutely new. It began 
to reproduce, to contract, to show irritability, and to take 
in foreign particles and transform them into new molecules 
of protoplasm. The world began to take on a new aspect 
when protoplasm came into it. One cannot continually 
look backward to chemical elements in treating of pro- 
toplasm ; he must look forward to the effects produced 
by protoplasm. 

Unity of self. So it is with a conscious being. Such 
a being is conditioned by sense organs and central nervous 
processes, but a description of these conditions does not 
exhaust the account. The self has become through organi- 
zation a unit in the world, capable of affecting in some 
measure the doings of this world. 

The self as an efficient cause. A conscious being is, ac- 
cordingly, different from a being not endowed with mind just 
in the degree in which the conscious being can produce 
effects which depend on consciousness. To deny the reality 
of the conscious self is to repudiate a scientific concept which 
is as fully justified as the concept solar system. 


Self as a valid scientific concept. Yet certain writers 
leny the right of science to deal with the idea of self. 
They say that the self is never seen as is the object which 
jives us a visual impression. They say that physical reality 
an be known, but the knowing self is something intangible 
,nd unapproachable by scientific methods. The difficulty in 
he whole situation is that the individual who is trying to 
xplain and understand himself sometimes loses sight of 
he central fact of his own mental life, as he explores the 
onditions which surround this central personality. The 
entral personality is taken so much for granted that sci- 
ntific description tends to deal with all that leads up to 
ersonality, and there it stops, finding its chief subjects 
f thought in these surrounding facts rather than in the 
entral result of all the organized conditions. Some day 
lie historian of thought will write it down as one of the 
urious fallacies of immature science that certain physiol- 
gists, biologists, and even psychologists, were satisfied to 
all their own personalities mere by-products, without es- 
[jntial significance in the world, just because they did not 
nd consciousness capable of description in the regular scien- 
fic formulas adopted for the discussion and explanation of 
xternal reality. 

One hardly knows how to find phrases in which to 
nswer those who hold consciousness to be less real and 
otent than physical forces. Certainly, nature has protected 
nd conserved consciousness throughout the whole develop- 
lent of the animal kingdom. Certainly, the world is dif- 
*rent because consciousness has been evolved. Certainly, 
Dnsciousness is no less real than are its conditions ; and, 
nally, consciousness is certainly much more directly 
pproachable to the student of science than is matter. 

Concept of unity. These are the statements which de- 
:ribe the psychologist's concept of the self. Such a con- 
spt is no less clear and well established than the concepts 


of all science. Indeed, it is from one's own ideas of him- 
self that the notion of external unities is derived. When 
one comes back time and time again to the same object and 
recognizes it as familiar and attributes to it a continuity 
which goes far beyond anything he can observe through his 
senses, he is projecting a concept of unity derived from his 
own experience into the world of outer realities. When sci- 
ence thinks of the earth as a unity, or of the universe as a 
unity, this is a concept, not a percept. The same kind of 
comprehensive generalization appears in the practical and 
scientific study of self. It is probably not true that animals 
recognize their own unity. Experience with them is, as it 
is with us, a succession of interrelated events, but the sur- 
vey of the total succession is not possible in the undeveloped 
animal consciousness. It is probably not true that children 
have any broad view of the unity of their personalities. The 
ability to remember is one of the most significant special 
experiences from which we derive the content with which to 
construct a broader self. The ultimate recognition of the most 
comprehensive unity is a conceptual rather than perceptual 
fact, even after memory has made its full contribution. 

The self a concept. One must be satisfied with a scien- 
tific description of the self. One can never see the self 
directly. To demand that the details of the total unity be 
filled in with a concrete image or illustration is to demand 
even more than natural science would demand, if it required 
a direct perceptual representation of its ultimate substances, 
such as the atoms. 



Disorganized personality in contrast with normal self. 

The discussions of the last chapter, as well as the detailed 
description of mental processes of various types, show how 
essential is the concept of self unity. This lesson is power- 
fully reenforced by considering certain abnormal states in 
which the unitary self gives way to disintegrating forces and 
leaves the self broken down and unable to play its part in 
the world. 

Illusions and hallucinations. Every form of mental pa- 
thology or abnormality is in some sense a case of malorgani- 
zation or disintegration. There are certain mild cases of 
irregularity which may be classed as forms of maladaptation, 
rather than distinctly pathological cases. Such are, for ex- 
ample, our geometrical illusions. As we saw in our earlier 
discussions, an illusion is always an incomplete organization 
of the sensations presented to the observer. Defects in or- 
ganization may be carried very much further in the case of 
a person who has what are known as hallucinations. An 
individual may, for example, have an irritation upon some 
part of the skin which, under normal conditions, would be 
neglected or, at most, treated as an inconvenient excitation 
of the part ; but if the organizations of mental life are un- 
stable because of some general diseased condition of the 
individual, this excitation in a certain part of the skin may 
become the center for a most abnormal combination of ex- 
periences and may lead to the development of a distinctly 
abnormal type of interpretation. Everything that suggests 



itself to the mind may be made subservient to this stimula- 
tion, until finally the person constructs an imaginary world, 
giving the abnormal excitation a value and importance which, 
in normal life, it could never have had. He may come to 
believe that he is made of glass or stone, or he may think 
that someone is attacking him with poisons or acids. These 
illustrations will serve to make clear what is meant by the 
statement that abnormal mental experiences arc always ex- 
periences which result from irregularities in organization, 
and commonly involve more or less disorganization or dis- 
sociation of the elements which should be combined. 

Sleep, the influence of drugs, hypnosis, and insanity as 
forms of disorganization. We may examine three distinct 
cases of dissociation in order to make clear in detail what 
is meant by mental disorganization. First, there is in sleep 
a form of normal suspension of central nervous activity which 
has been provided by nature for the purpose of recuperating 
the individual. This nervous condition is accompanied by a 
temporary interruption of normal conscious processes. Sec- 
ond, there are certain forms of dissociation and partial re- 
construction which are very similar in character to sleep, but 
do not serve the purposes of recuperation as does normal 
sleep. The conditions here referred to may be induced by 
the use of drugs or by certain other devices, conspicuous 
among which are the methods of inducing hypnosis. Finally, 
the dissociations and partial reconstructions, which are tem- 
porary in hypnosis and after the use of certain drugs, may 
appear in a great variety of relatively permanent forms in 
the different types of insanity. One or two of these typical 
forms of insanity will be referred to later, in order to 
exemplify the conditions which result from permanent 

The physiological conditions of sleep. The physiological 
conditions which present themselves in the nervous system 
during sleep are not fully understood, but their general 



character can be described with sufficient clearness for our 
purposes. In the first place, the condition of fatigue in the 
nerve cell has been found to be a condition of somewhat 
depleted tissue in the cell body. There are also certain 
chemical changes resulting from fatigue. These are demon- 
strated by the different degrees 
to which fatigued and normal 
cells respectively take on the 
coloring substances which are 
used in staining microscopic 
sections of the tissue. The 
protoplasm of the fatigued 
cells, as seen from Fig. 58, is 
in part exhausted as a result 
of the processes of stimulation 
through which they have passed. 
Sleep must be a condition in 
which these cells are supplied 
with nutrition and return to 
their normal state of energy 
and activity. During the period 
of sleep, each cell seems to be 
capable of insulating itself from 
the neighboring parts of the 
nervous system. There are 
some extreme conditions, prob- 
ably pathological in character, 
in which the dendrites of the 
nerve cells curl up and form, 
instead of extending branches, little knotty balls across 
which stimulations cannot easily pass. This curling up of 
the dendrites is probably a very much more radical change 
than occurs under the ordinary conditions of sleep. The 
synapses, or interlacing of fibers, which connect a cell 
with other cells or incoming fibers, are interrupted in most 

FIG. 58. Fatigued cells 

Two sections A and B from the first 
thoracic spinal ganglion of a cat. B is 
from the ganglion which has been elec- 
trically stimulated through its nerve 
for five hours. A is from a correspond- 
ing resting ganglion. The nuclei N of 
the fatigued cells are seen to take a 
darker stain and to be very irregular 
in outline. The general protoplasm of 
the cell bodies is also less uniform in 
density in the fatigued cells. (After 


cases, not by any gross movement of the dendrites but rather 
by some chemical change in the tissue which makes it 
difficult for the stimulation to pass across from one cell to 
another. There are known chemical substances which affect 
primarily the synapses and prevent stimulations from being 
transmitted from cell to cell. All of these indications go to 
show that the nerve cell, when it enters on the process of 
recuperation, tends to give up its normal transmitting func- 
tion, and devotes itself for the time being to the processes 
of building up tissue. 

The closing of avenues of stimulation in sleep. The ex- 
ternal characteristics of a sleeping individual are clearly 
intelligible in terms of the physiological changes which have 
been described. In the first place, the individual becomes 
less and less susceptible to stimulations from the outside 
world. This means that when any form of external energy 
acts on the nervous system, it finds the nervous system rela- 
tively inert. The receiving organs are closed and their cells 
are probably in a chemical condition unfavorable to any vig- 
orous activity. Even when stimulations are received at the 
periphery and are transmitted to the central nervous system, 
they make headway through the tissues with the greatest 
difficulty. They do not follow the well-defined paths which 
are used in normal life, but are diffused throughout the 
whole organ. 

Various degrees of dissociation. The condition of the 
individual need not be a condition of complete sleep in 
order to show this inertness of the nervous system. There 
are many conditions of fatigue in which the nervous system 
shows, before sleep sets in, more or less of a tendency to 
resist external stimulation. Furthermore, the different stages 
of sleep are by no means equal in their degree of dissocia- 
tion. This has been shown by experiments in which the 
amount of noise necessary to arouse a sleeping individual 
has been made the measure of the intensity of sleep. The 



result of such experiments is to show that a person goes to 
sleep rapidly and profoundly during the early part of the 
night, and from this time on gradually comes back to a con- 
dition of susceptibility to stimulation. Fig. 59 shows a sleep 
curve of the kind which results from these experiments. 

r .5 78 

FIG. 59. Curve showing the intensity of sound necessary to awaken a 
sleeper at different periods of sleep 

Along the homontal line are represented the hours of sleep ; along the vertical, the 
relative intensities of sound. Thus, at the end of the first half hour an intensity of 
sound somewhat over six hundred is necessary to awaken the sleeper. At the end 
of two hours the intensity of sound is approximately one hundred. The curve indi- 
cates that the sleeper falls rapidly into a profound sleep and then gradually comes 
into a condition of very light slumber preceding for a long time the waking. (After 


The curve rises rapidly, indicating, as stated, that the amount 
of stimulation necessary to arouse the nervous system in- 
creases rapidly in the early hours of sleep; it falls off 
gradually toward the end, indicating a gradual waking of 
the subject. 

Dissociation in the central processes. Not only are the 
cells of the sleeper's nervous system impervious to external 
stimulation, but they are uncoupled in such a way that the 
stimulations which succeed in entering the nervous system 


do not follow the ordinary paths of discharge. This uncoup- 
ling of the central nerve cells does not take place in equal 
degree in all parts of the nervous system. The large cells 
of the spinal cord are able to resist the effects of fatigue, 
and the spinal cord may be said never to sleep under normal 
conditions. For this reason, stimulations which reach the 
spinal cord from the surface of the body are always trans- 
formed into reflex impulses and sent to the muscles of the 
trunk and limbs. The spinal cord is in this case uncoupled, 
not within itself, but only with reference to the higher centers. 
The reflexes are very much simpler in form and more likely 
to appear under these conditions than when the stimulus has 
an open path to the higher centers. Thus a cold or uncom- 
fortable hand will always be moved reflexly in sleep. The 
medulla, like the cord, seems to be able to resist, to a great 
extent, the tendencies toward fatigue, for many of the organic 
processes, such as circulation and respiration, are maintained 
through the nerve centers in the medulla, while the rest of 
the nervous system is closed to external stimulation and to 
any well-ordered activities. 

Dreams as dissociated groups of ideas. One effect of the 
uncoupling of the various nerve tracts in the organs of the 
central nervous system above the medulla is that any proc- 
esses which take place in these higher organs because of 
strong stimulations, or Because of some abnormal excita- 
bility in the nervous system, are fleeting and irregular. The 
higher centers probably do not all of them sink into the 
same degree of inactivity even in a normal individual, and 
the slightest abnormality may result in a heightened activity 
in certain parts. The facts of consciousness which corre- 
spond to these irregular, detached activities in the central 
nervous system during sleep are easily understood when it 
is recognized that the nervous system is acting not as a 
single organized system but as a disorganized group of 
centers. To put the matter in terms of experience, one may 


say that an idea which presents itself during sleep is not 
related to the general body of ideas by which the experi- 
ences of ordinary life are checked and held under criticism. 
If, in ordinary life, the idea suggests itself to some indi- 
vidual that he has enormous possessions, he is immediately 
reminded by the evidences of his senses and by the familiar 
surroundings and limitations of his sphere of action that the 
idea is merely a subjective imagination. If, on the other 
hand, one should have this idea in his dreams, under con- 
ditions which would remove it from all restricting relations, 
it would obviously be compelling in its force and would be 
accepted by consciousness as an unqualified and unlimited 
truth. It would be dissociated from the other ideas which 
fill normal consciousness, and this dissociation would deter- 
mine its character in such a way as to make it distinctly 
different from the processes of coherent thought built up in 
normal life. 

Dreams impressive only because they are uncriticized. 
It will be seen from such considerations as these that a 
mature individual is brought in his sleep into a condition 
somewhat similar to that exhibited in the irregular and un- 
restrained imaginings of children. The young child con- 
structs imaginations and is quite unable to criticize them 
because of his lack of experience and because of the lack of 
organization within his experience. The lines of organiza- 
tion are not laid down in the child; in the dreaming adult, 
though systems of ideas have been built up, they are for 
the time being interrupted, and the processes of mental life 
lapse into unsystematic and uncritical forms. There is, for 
this reason, a certain freedom from all kinds of restraint, 
which accounts for the highly erratic character of dreams. 

Motor processes suspended by dissociations in sleep. The 
third characteristic of sleep follows naturally from these 
which we have been discussing. Muscular movements are 
almost completely suspended in normal sleep. Ths musdes 


relax more than they do in any condition of waking life, just 
because the nervous system sends only very much reduced 
stimulations to the muscles, and, as we have repeatedly 
seen, the muscles are quite unable to perform their work 
when they' are not stimulated by the nerves. The few 
straggling stimulations which succeed in getting through 
the nervous system to the muscles are lower reflexes or they 
are irregular and without coordination. The movements 
which appear arc, therefore, often more incoherent than the 
fleeting dream experiences which accompany the activities 
in the central nervous organs. Indeed, in most cases, any 
intense movements of the muscles during sleep indicate a 
distinctly abnormal condition and are closely related in char- 
acter to the irregular coordinations which appear in certain 
forms of drug poisoning. 

Narcotic drugs dissociative in their effects. The discus- 
sion of the phenomena which attend the use of drugs will 
aid in the understanding of what has been said about sleep. 
It is a familiar fact that certain narcotics produce a condi- 
tion very closely related to sleep. The narcotic drug closes 
the avenues of sensory reception, reduces central activity or 
renders its processes irregular and incoherent, and suspends 
muscular contraction. If the drug is taken in a relatively 
small dose, so that its effect upon the nervous system is 
slight, these various effects may be produced in slight 
degree only. The effect in this case will be most marked 
in the irregularity of ideas and in the incoordination of 
the movements. 

Effect of alcohol on the nervous system. A familiar effect 
of a drug is the intoxication which is produced by alcohol. 
The chemical condition of nerve cells and consequently the 
relations between them are in some way affected by alcohol, 
and the stimulations are interrupted or become irregular 
in their transmission through the tissues. The fact that a 
man under the influence of alcohol sees things moving 


irregularly, or sees them double, depends upon the incoordina- 
tion of the muscles of the eyes. The fact that he is unable 
to walk steadily shows the incoordination of the muscles of 
the legs. There is a corresponding irregularity in the flow of 
his ideas ; and his credulousness for the ideas which suggest 
themselves to him is analogous to the ordinary credulous- 
ness of a dreaming sleeper. The imperviousness of such an 
individual to the stimulations of the outside world is also 
a well-known fact. 

Overexcitation is also dissociative. In the case of any 
one of the drugs which produces dissociative conditions in 
the nervous system, the condition may be overcome by the 
ordinary processes of recuperation by which the organism 
throws out the drug. In some cases the effort of the organ- 
ism to restore the normal condition leads to a reaction which 
is abnormally intense. We may then have for a time, as a 
result of reaction to the drug, a state of hypersensitivity and 
a more vigorous activity within the central nervous system 
and in the muscles. The dissociating effects of such intense 
activity in the nervous system may be, so far as consciousness 
and muscular coordination are concerned, quite as abnormal 
as the depressing effects of fatigue or complete suspension 
of nervous activity. Thus, if the stimulations coming to the 
central nervous system are much increased in their intensity 
because the nervous tissue has been thrown into a condition 
of heightened activity, there may be an irregularity in the 
central nervous processes due to the abnormally strong cur- 
rents of excitation and to the impossibility of restraining 
these currents of stimulation within the ordinary channels 
of connection and discharge. The disorganization here is 
like the disorganized behavior of a stream that overflows 
its banks. 

Toxic effects of certain diseases. There are certain condi- 
tions produced in nature which are quite analogous to those 
which are produced by drugs. Such conditions appear in 


fevers when the organism is under the influence of certain 
toxic substances produced by the organism itself or by 
bacteria lodged in the body ; under such conditions the 
nervous system is rendered hypersensitive through the 
chemical action of these foreign substances on the tissues. 
The delirium of the fever patient presents clearly the picture 
of too intense activity in the central nervous system, and the 
muscular activity of such an individual is directly related to 
his irregular and excessive central processes. Such a person 
may also be excessively sensitive to slight sounds or other 
irritations of the organs of sense. 

These negative cases as evidences of the relation between 
normal consciousness and organization. These different 
cases show the relation between nervous organization and 
mental organization, and by their negative characteristics con- 
firm' the discussions of the preceding chapters, in which it 
has been maintained that normal mental life is a continuous 
process of integration and organization. 

Hypnosis a form of dissociation closely allied to sleep. 
The condition known as hypnosis has long been the source 
of superstitious wonder, and much has been said and written 
in regard to it which would tend to increase the mystery 
which attaches to it. In many respects it is a condition 
closely related to normal sleep. On the other hand, it has 
certain peculiar characteristics which differentiate it from 
ordinary sleep. These peculiarities can, however, be fully 
understood tinder the formula adopted in explanation of 
normal sleep, provided that formula is slightly modified to 
include certain specialized forms of dissociation. 

Hypnosis as partial dissociation. While normal sleep in- 
volves the uncoupling or dissociation of the nervous ele- 
ments, especially of the type which suspends activity in 
the higher centers, hypnosis involves a dissociation which 
is partial and leaves a part of the higher centers in action. 
To put the matter in simple terms, we may say that in 


normal sleep the cerebrum is dissociated from the- lower 
centers, and all the centers in the cerebrum are dissociated 
from each other; whereas, in hypnosis only a part of the 
cerebrum is dissociated from the lower centers. The 
remaining part of the cerebrum continues to carry on its 
activities and, indeed, profits by the cessation of activity 
in the dormant portion, for the active part of the nervous 
system is, in such a case as this, supplied with an unusually 
large amount of blood, and its activity may reach a much 
higher level of intensity, because of this superior nutritive 
supply and because of the concentration of all of the nerv- 
ous activity in one region. Such a crude statement as this 
is undoubtedly too simple in its terms, and yet it represents 
the situation in principle. 

Methods of inducing hypnosis. The way in which the con- 
dition of partial or hypnotic dissociation is produced in the 
nervous system differs with the practice of different hypno- 
tizers. One of the characteristic methods of producing 
hypnosis is to require the subject to gaze at some bright 
object until a kind of partial stupor comes over him. He 
may then be aroused to activity through the sense of hear- 
ing. The ideas which he receives and the activities which 
he performs have, under these conditions, many of the 
characteristics of dissociation. Another way of producing 
hypnosis is to soothe the subject into a sleeplike condition. 
Stroking the forehead or the face is very commonly prac- 
ticed by hypnotizers. Here again, the appeal to the subject, 
after the dormant condition has set in, is through the sense 
of hearing or even through the sense of vision. 

Hypnosis more readily induced after it has once been estab- 
lished in a subject. When a subject has been frequently 
hypnotized, it is possible to reproduce the hypnotic condi- 
tion without elaborate preliminaries. The subject acquires 
what may be called a habit of dissociation. A simple order 
from the hypnotizer is enough to throw the subject into the 


condition. Sometimes the habit is carried to such an ex- 
tent that the subject is able to throw himself into the hyp- 
notic condition. Such self-induced hypnosis is known as 
auto-hypnosis. The ability to produce the hypnotic state 
in the subject does not depend upon any peculiar powers 
on the part of the hypnotizer ; it depends rather upon his 
ability so to influence his subject that the condition of par- 
tial sleep described shall be induced. The essential condi- 
tion with which the subject himself must comply, in order 
to come under *the influence of a hypnotizer, is that he con- 
centrate his attention. The only persons who cannot be 
hypnotized are young children, idiots, and insane persons, 
all of whom are unable to concentrate attention. This state- 
ment effectually disposes of the popular belief that only 
weak-minded persons can be hypnotized. The most effec- 
tive method of avoiding hypnosis is to scatter attention as 
much as possible over a great variety of objects. Concen- 
tration of attention is always favorable to hypnosis and 
allied conditions. The audience which gives close attention 
to a speaker or performer is susceptible to a species of 
hypnosis ; while, on the other hand, there is no danger of 
hypnosis in a distracted audience. The methods of induc- 
ing hypnosis have been accidentally discovered from time 
to time by performers who are then able to give striking 
exhibitions of their discovery. Many oriental jugglers be- 
gin their performance, the success of which undoubtedly 
depends upon their hypnotic influence over their audiences, 
with a dance in which the body of the performer is moved 
with a gradually increasing speed, which inevitably induces 
a gradually increased concentration of attention on the part 
of the observer. When this dance grows more and more 
rapid and more and more engaging to the attention, the 
observer is completely mastered and the main performance 
may be undertaken. The hypnotic influence of such a dance 
is very frequently augmented by the burning of incense, 


which has more or less of a narcotic effect upon the ob- 
servers. In like manner, certain animals are probably 
drawn into a hypnotic state by the movement of snakes. 
This has frequently been reported in the case of birds and 

Various characteristics of the hypnotized subject. When 
the hypnotic state has been produced, the phenomena ex- 
hibited are of two distinct types. First, there is a suspen- 
sion of certain activities, and, second, there is an abnormal 
heightening of other activities. This may be seen with 
reference to the reception of sensory stimulations. Certain 
stimulations arc no longer received by the hypnotized sub- 
ject. For this reason the condition has sometimes been 
used by savage tribes for surgical purposes, exactly as in 
modern life we use drugs which will produce a dissociation 
of the nervous system and thus prevent pain from exces- 
sive external stimulation. On the other hand, certain other 
senses may be opened to stimulation. A hypnotized subject 
may be wholly anaesthetic in his skin, while still retaining 
the ability to receive impressions through certain of his 
other senses. Indeed, the concentration of nervous activity 
in certain particular senses results in such a heightening 
of their ability to receive impressions that the subject may 
perform most astonishing feats of sensory receptivity. He 
may hear very faint sounds or he may see remote visual 
objects. It is to be noted that this hypersesthesia of the 
senses is not so extraordinary as it would at first sight seem 
to be. We all become hypersesthetic when we concentrate 
attention in any direction. If one is listening for an im- 
portant signal or watching for some object which is of 
great importance to him, he will be using his nervous 
energy in the emphasized direction and will be correspond- 
ingly impervious to impressions from other sources. The 
conditions in hypnosis are merely exaggerations of those 
which appear in ordinary life. 


Ideas not subjected to criticism in hypnosis. Turning 
from the sensory processes to the central processes, we 
find again that certain activities are entirely in abeyance, 
while others are much intensified. If, for example, it is 
suggested to a hypnotized subject that he is an animal 
instead of a human being, the suggested idea may take such 
large possession of him as to command his whole attention 
and guide his activity. If a normal individual is told that 
he is an animal, he immediately brings to bear upon the 
suggested idea a great variety of incompatible experiences, 
which make it clear that the statement is false and unaccept- 
able. In the case of the hypnotized subject, very much as 
in the case of the dreamer, the corrective ideas, which con- 
stitute the fabric of normal life, are absent, so that the 
single idea takes full possession of the mind and commands 
belief as the accepted content of consciousness. This credu- 
lousness of the hypnotic consciousness is described by say- 
ing that the subject is very open to suggestion. Anything 
that is said to him will be accepted, and any form of inter- 
pretation of experience which is offered to him will be 
taken up without serious question and without any effort 
on his part to criticize the ideas which have been given him 
by the hypnotizer. Suggestibility has very frequently been 
emphasized to the exclusion of the converse fact that the 
hypnotized subject is quite incapable of subjecting any ideas 
to critical comparison. So also the positive increase in 
sensitivity has been the impressive fact ; the diminution of 
sensibility has often been overlooked. The negative con- 
siderations are, however, essential to a complete under- 
standing of the case, just as the negative considerations 
are of importance if we would understand the credulousness 
exhibited in dreams. 

Dual personalities in hypnosis. The central nervous con- 
ditions which are induced in hypnosis are sometimes suffi- 
ciently unstable to produce the most complex phenomena. 


It is sometimes found that the dissociated parts of the cere- 
brum are not only dissociated from each other, but they 
are also, to a certain extent, capable of independent action. 
Thus, while one part of the cerebrum seems to be dealing 
with impressions received through the sense of hearing, 
another part may be engaged in responding to tactual im- 
pressions. Or, the case may be rendered even more com- 
plicated by the fact that the impressions coming from one 
ear seem to serve as stimulations for certain activities, while 
auditory impressions received on the opposite side of the 
body are effective in producing an entirely different set of 
experiences and responses. There result in such cases 
what are known as dual and multiple personalities. By 
personality, as the term is used in such cases, is meant 
any organized group or system of ideas and activities. 
The various groups of systematized activities and ideas 
which exist side by side in a hypnotized subject owe 
their separation to nervous and mental dissociation ; each 
personality is, therefore, a relatively less complex system 
than that which exists when the whole cerebrum is acting 
as a single organ. The division of an individual into a 
number of systems of organization appears in other states 
than the hypnotic state, and it may result in certain per- 
manent or certain temporary disruptions of personality, 
which have been noted in such stories as that of Dr. Jekyll 
and Mr. Hyde. 

Dual personalities in other than hypnotic conditions. 
From time to time one reads of a case of lapse in memory 
which amounts to a dissociation of personality. A man for- 
gets who he is or what business he has been following. He 
is sufficiently normal in his general organization to respond 
to a great variety of impressions in a regular fashion, but 
the complex structure of mental life breaks down and 
the man is only partly reconstructed in the second self. 
Tertiary and quaternary personalities may appear in all 


possible combinations. The secondary or tertiary personality 
may know its fellows, but may be itself quite forgotten. 
Several cases have been described in which personality B 
knows not only its own acts and emotions but also the acts 
and emotions of the other personality A. Sometimes B not 
only knows but heartily dislikes A. Sometimes two per- 
sonalities exist simultaneously within the same body and 
seem to have separate lives and characters. The writer 
knew of a case of a young man who was the object of 
superstitious wonder in the village in which he lived, be- 
cause he had two personalities. These two personalities 
knew each other and held long discussions with each other. 
Often, when they came to a turn in the road, they dis- 
agreed with each other as to the direction in which their 
body should move, and the passer-by could see the abnormal 
man mumbling an argument between his two selves. 

Dual and multiple personalities analogous to the various 
selves of normal life. The details of such cases are baffling 
in the extreme, but nothing can be clearer from our earlier 
studies than the general formula of dissociation, with the 
added fact of partial organization around different centers. 
The matter becomes more intelligible if we remember that 
even in ordinary life there is a subdivision of experience 
into different systems. We distinguish, even in common 
parlance, between the business self, the social self, and so 
on. Each one of these selves is only partially related to the 
other systems of experience and forms of behavior. The 
man who is buried in the details of a business transaction 
is just as oblivious to considerations of a literary sort as the 
hypnotized subject is oblivious to a certain group of possible 
experiences. We do not call the ordinary absorption of the 
self in business a case of multiple personality, because 
the neglected personality in the case of the business man 
is not so remote but that it can be immediately called out, 
if he turns his attention to some literary considerations. 


The normal individual is capable of transferring his atten- 
tion and interest from center to center according as the 
external environment demands, while the hypnotized subject 
or abnormal person is, through dissociation, quite incapable 
of a rapid transfer of attention or of correlating the different 
phases of his experience. 

Hypnosis a transient condition, insanity permanent. We 
shall return to the discussion of multiple personality under 
the general head of insanity, for the fundamental distinction 
between insanity and hypnosis is to be found in the degree 
of permanency which is attained in the former state, as 
contrasted with the more transient character of the hypnotic 

Movements sometimes normal in hypnosis, because the 
lower centers are not dissociated. In the meantime, it is 
necessary to add a few comments on the motor activities of 
hypnotized subjects. These motor activities frequently ex- 
hibit little or no departure from the ordinary coordinations 
of normal life. The hypnotized subject is capable of walk- 
ing, often of writing or producing certain other complex 
forms of movement. Such continuation of the bodily coordi- 
nations is explicable on the ground that the lower centers of 
the nervous system are not dissociated by the changes that 
take place in the higher centers. Whenever the higher 
centers are able to send stimulations to the lower centers, 
these lower centers are capable of responding with their 
usual degree of coordination. The lack of organization is 
exhibited rather in the inability to maintain a normal bal- 
ance between the various centers which call the lower centers 
into play. It is to be noted, however, that the movements 
of hypnotized subjects sometimes indicate by their clumsi- 
ness and lack of precision that the disintegrating force has 
affected certain of the motor channels as well as the central 
organizations. This is especially true when the attempted 
act involves a complicated coordination. 


The after-effects of hypnosis tend to become permanent. 
There is one group of facts in hypnosis which should 
perhaps be made the subject of special comments. The 
suggestions received by the hypnotized subject may, in 
some cases, be carried over so as to become operative in a 
later period, after the subject has apparently recovered from 
the hypnotic trance. Such after-effects are known as post- 
hypnotic effects, and the suggestions are described as 
post-hypnotic suggestions. Even more significant is the fact 
that after-effects of the hypnotic trance are of a general 
kind. It is a fact that the effect of the hypnotic state is in 
the direction of a perpetuation of dissociative tendencies. 
Sleep is transient and leads to a more vigorous form of 
activity after it is over. Hypnosis, on the other hand, tends 
not to restore the nervous system to a more vigorous condi- 
tion but to perpetuate dissociation. This is due to the fact 
that sleep is negative, while hypnosis is positive in certain 
of its phases, in that it trains certain centers to act without 
reference to others. It therefore operates by virtue of its 
positive phases toward permanent disorganization. It is for 
such reasons as these that the use of hypnosis is in general 
to be avoided. The disorganizing effects of hypnosis are of 
the same general type as the disrupting tendencies of certain 
drugs. The individual, who with sufficient frequency comes 
under the influence of these drugs or of hypnosis, will 
ultimately settle into a state of nervous disorganization from 
which it will be quite impossible for him to recover, even 
when recovery is demanded for the purposes of normal 
life. Hypnosis is not utilized by reputable practitioners, 
because its ultimate effects are not as readily controllable 
as are the effects even of the narcotic drugs ; and there is 
no justification whatever for the use of hypnosis as a means 
of amusement, any more than there would be for using a 
strong narcotic drug to bring an individual into a condition 
which would make him a source of entertainment. 


Insanity a permanent form of disorganization, intro- 
duced in many cases by dissociation and settling into an 
abnormal reorganization. As has been indicated in the 
earlier paragraphs, insanity is a form of relatively permanent 
dissociation. Certain forms of delirium, which have been 
referred to before, furnish the best introduction to the study 
of insanity. In delirium the subject is so highly excitable 
that the normal avenues of stimulation and discharge are 
for the time being completely disrupted, and the currents 
of nervous activity and the corresponding facts of experience 
are dissociated. As delirium disappears and gives place to 
the usual intensity of nervous activity the individual may 
return to the earlier normal condition or, on the other 
hand, there may be left behind a permanent abnormal state, 
because the earlier forms of organization are not fully 
restored. One of the most characteristic symptoms of all 
forms of insanity is found to be the existence of certain 
hallucinations or fundamental abnormalities in the subject's 
world of ideas. The insane person believes himself to be 
Julius Caesar or some Biblical character, or even some 
divinity. There is no difficulty in recognizing the fact that 
the idea of transferred identity may come into the mind of 
any normal individual. It is, however, in the case of a 
normal individual immediately criticized and abandoned, 
because of its incompatibility with the person's general 
knowledge of the world and his place in it. When the 
compact organization which has been built up in normal 
experiences has once given way, and the idea that one is 
Julius Caesar or some other character has presented itself 
as a center of reconstruction in the midst of the resulting 
chaos, there is a possibility of an abnormal reorganization 
of experience. The individual is no longer restrained by 
that system of ideas which has been laboriously built up 
through contact with the world ; the result is that the whole 
later ideational life of the individual loses its adaptation to 


the real world. The characteristic fact in certain cases 
of insanity is, accordingly, not describable in simple terms 
of dissociation ; it is rather to be defined in terms of disso- 
ciation with an abnormal association or integration following 
upon the breaking down of the normal system. In other 
cases, disintegration is the more obvious fact. The individual 
simply loses control of his ideas, and his mind seems to be 
flooded with an incoherent mass of experience. His words 
reflect this incoherency of ideas, and his behavior indicates 
an absence of self-control. Such disintegrated forms of 
consciousness and behavior commonly appear in the last 
stages of almost every kind of insanity, even where there 
has been for a time reorganization about an abnormal center. 
Melancholia as a typical form of dissociation. One of 
the very general forms of dissociative abnormality is that 
which appears in so-called melancholia. In melancholia 
there is a general reduction of all the bodily activities, 
including the activities in the nervous system. The subject 
becomes phlegmatic and depressed in all his functions. 
The whole feeling tone of experience takes on a marked 
disagreeable character, which can be explained in terms of 
our earlier discussion of feeling by saying that the individual 
does not arouse himself easily to respond to any form of 
stimulation, and when his nervous system is in any way 
aroused by powerful external excitation, the reaction upon 
the stimulus is so laborious and contrary to his tendencies 
and mood that he has a strong feeling tone of a disagree- 
able type. The ideas which such a subject has are often 
organized about each other in a way that furnishes a kind 
of false explanation of the subject's mood. The melancholic 
subject has certain grievances against the world. Sometimes 
these grievances are of a trivial character and make it clear 
that the grievance could not have been the exciting cause of 
the subject's condition. Sometimes the grievance is more 
real and furnishes an apparent ground for the condition. 


Even in such a case it is to be said that the person's 
physical condition must have developed into one of general 
debility before the apparent cause of his mental conditions 
could have become the source of abnormal melancholia. 
The distinction between a passing case of depression in 
normal life and melancholia is that passing depression is 
temporary, and nature rebounds from it in such a way as 
to produce normal conditions after the depressing circum- 
stances are past. In the case of melancholia the depressing 
tendencies become permanent, and it is this permanency 
rather than the fact of depression or its corresponding 
nervous conditions which constitutes the characteristic fact 
in insanity. Indeed, one can find almost every possible 
grade of transition from normal life to extreme abnormality. 
The result is that those who have made a special study of 
these transitions, and those whose attention is for the first 
time called to the possibility of such transition, are likely 
to indulge in the extravagant statement that all persons are 
at times or on certain subjects more or less insane. It is 
undoubtedly true that all persons do depart at times from 
the type of mental and bodily organization which constitutes 
normal life, but unless these states become fixed and lead 
to distorted and unadapted forms of behavior, they should 
not be classified as cases of insanity. 

Excessive excitation as a second typical case of insanity. 
The opposite tendency to the melancholic condition just 
described appears in certain cases of excessive excitation. 
A person when abnormally excited is very frequently pos- 
sessed of excessive bodily strength. This is not due to any 
change in the structure of his muscles, but rather to the 
fact that the nervous system which is in control of the mus- 
cles is sending to the active organs stimulations of excessive 
intensity. There are numerous cases in normal life which 
will help us to understand this fact. If an individual is 
fatigued, encouragement and stimulation from the outside 


world will appreciably increase his ability to execute muscular 
movements. In the same way an individual may be so 
stimulated by abnormal substances in the blood that his 
whole nervous behavior is raised to a high level of activity 
and the motor discharges are abnormally intense. The 
muscular activity of such a person is typical of his whole 
condition. His ideas come in an overwhelming flood and 
lead him into the most extravagant excesses of imagination 
and lack of self-control. 

Fundamental ^disturbances of instinctive and emotional 
life. Of late much attention has been given to the fact that 
in all cases of dissociation the fundamental instincts assert 
themselves and play a leading part in the behavior and 
ideation of the abnormal individual. For example, there 
are types of fear which haunt a patient and distract him 
from all normal modes of thought and life. Or the sex 
instinct becomes dominant, or the food instinct leads to 
irregular or irrational behavior. The mode of treatment 
which is adopted in such cases aims in part to restore 
normal nutritive conditions and then proceeds on the as- 
sumption that the individual must be started on the road to 
a reconstruction of his mental world. Often the shortest 
route to this latter goal is to bring out in explicit detail some 
of the deep-seated dissociations. Thus, the person who is 
suffering from terror is made aware of the sources of his 
terror and is encouraged to reorganize his thinking and his 
attitudes toward the object of his dissociation. The abnormal 
state can be compared to physical clumsiness. The indi- 
vidual whose muscles will not coordinate must develop 
physical cooperation of the organs of his body by using 
them in a well-ordered, systematic fashion. So with the 
person suffering from mental incoordination, there must be 
a well-directed effort at mental recoordination. 

Relation of psychiatry to psychology. These illustrations 
must suffice for our present purposes. There are all possible 


combinations of disintegration and reorganization exhibited 
in insanity. There is a science known as psychiatry which 
deals with these forms of dissociation and abnormal associ- 
ation, and there is a large field of practical observation and 
study open here to the trained scientist. The chief lesson 
for our general science is that the normal processes are 
processes of integration leading to forms of association which 
contribute to adaptation. There are frequently illustrations 
which throw light upon important principles of normal asso- 
ciation, to be found by making a careful study of the facts 
of dissociation, but in general the explanation of abnormal 
states is made easier by a careful examination of normal 
processes rather than the reverse. It does not follow that 
dissociation will be along the same lines as association, and 
the effort to work out the details of one by the other often 
leads to fallacies. The general tendency of normal life is, 
however, obviously in the direction of adaptive organization ; 
the tendency of sleep, hypnosis, and insanity, on -the other 
hand, is in the opposite direction. The particular path fol- 
lowed in each case can be defined only through empirical 
examination of the case. 



Voluntary action a special form of behavior. Though the 
preceding chapters have discussed at length many of the 
relations between bodily activity and mental processes, they 
have not dealt specifically with that form of behavior which 
is described by the term "voluntary choice." One may 
reach out and pick up the book before him, or one may 
decide not to touch the book. One may take the pen and 
sign a contract, or one may refuse to sign. The whole per- 
sonality enters into such a decision, and we recognize both 
in ordinary thought and in scientific consideration of the 
matter that the ability to choose, especially the ability to 
choose wisely and consistently, is the supreme power culti- 
vated in the development of the individual. Our penal code 
recognizes the fact that an immature child is not responsible 
for his actions in the measure in which a full-grown man is 
responsible. Those who are mentally defective are exempt 
from the penalties of the law just in the degree in which 
they fall short of normal development. These and other 
illustrations of common practice show that voluntary choice 
is the fullest expression of the developed normal self. 

Instinctive behavior different from voluntary action. The 
explanation of voluntary action depends on a series of dis- 
tinctions which have been implied in earlier chapters. Thus 
instinctive acts are not forms of voluntary behavior. For 
example, the infant swallows not from deliberate choice but 
because nature has provided a nervous and muscular mecha- 
nism which responds promptly to the proper sensory stimulus. 



One has only to think of the cases in adult experience where 
the swallowing reflex acts when the swallower would gladly 
check it. Furthermore, most people do not know that they 
cannot carry out the act of swallowing without a proper sen- 
sory stimulus. Let one try the experiment of swallowing 
five times in succession. All the saliva in the mouth will 
have been swallowed the second or third time the effort is 
made, and after that the mechanism refuses to work until 
more sensory stimulation is supplied. Instinctive acts are 
therefore different from volitions. Sometimes we can volun- 
tarily check one of these acts, although here our powers are 
limited, and we can in some measure decide when an act 
provided by the inherited nervous mechanism shall be 
allowed to take place, but here again our control is limited 
as shown in the example given above. 

Impulsive acts distinct from higher forms of voluntary 
action. If we follow the development of an individual from 
infancy, we find that there are other forms of behavior which 
resemble the instincts in that they are not fully under con- 
trol. For this general class of acts we commonly use the 
term " impulsive acts." It is almost impossible not to imi- 
tate a yawn ; it is very difficult not to look around when one 
hears an unfamiliar noise. The impulse to take food when 
one is hungry is very strong; the impulse to strike back 
when one is struck is so strong that the interpretation of re- 
sponsibility is always based on an examination of provocation. 

Impulsive acts as phases of general muscular tension. 
Impulsive acts can be explained by formulas which have 
been discussed at length in earlier chapters. It was there 
pointed out that the whole organism is constantly at a higher 
or lower level of tension. The muscles of a waking person 
are always on the stretch. There are internal activities of 
respiration and circulation and digestion which are not only 
in a state of tension but are in an actual state of continuous 
operation. The eyes are usually focused on some object; 


the hand is seldom at rest and still more seldom in a state 
of relaxation. This state of muscular tension and internal 
action is due to the continuous stream of nervous impulses 
which flow out to the active organs. The outgoing motor 
impulses are in turn the results of the sensory stimulations 
of the moment and the reverberations of sensory impressions 
which are circulating through the massive cerebrum. 

Impulsive acts explicable through nervous organization. 
An impulsive act exhibits in its particular form the past 
experience and training of the individual. We often judge 
of a person's character and education by his impulsive acts. 
The spy who was betrayed by his impulsive and wholly 
uncontrolled response to a sudden military order to stand 
to attention exhibited his training by his very lack of vol- 
untary control. One may guide his impulses in some 
measure by the slow process of changing his habits. If 
one tends to look up from his work every time a shadow 
passes over his desk, one may overcome this tendency by self- 
discipline ; but in that case the inadvertent lapses into the 
old mode of looking up will furnish the strongest evidence 
of the difference between impulse and voluntary control. 

Impulse comparable to involuntary attention. The term 
"impulse" as applied to behavior finds a parallel in certain 
terms which are used in describing strictly mental processes. 
One tends to look at any object that moves through the 
edge of the field of vision. This is an impulsive tendency. 
On the psychical side we describe this fact by saying that 
moving objects in the edge of the field of vision attract 
involuntary attention. Attention of the involuntary type is 
then contrasted with certain higher types of attention 
which are designated as voluntary. Thus, when one keeps 
his eyes fixed steadily on the signal which he is set to 
watch in spite of distracting appeals to his involuntary 
attention, we speak of his effort as an exhibition of volun- 
tary choice or self-control. 


Impulse and involuntary attention related to perception 
and habit. It is hardly necessary to elaborate here the 
matter of the relation of impulsive activity to perception 
and habit. Our earlier chapters have abundantly illustrated 
this relation and shown its importance. We have, however, 
reached the point where we must face the problem of the 
distinction between voluntary attention and all lower forms of 
perception and thought, and the problem of the distinction 
between voluntary action and impulse. 

Simple case of choice. Perhaps the best method of 
making progress toward the solution of our problem is to 
analyze one of the simpler cases of volition. For this pur- 
pose let us consider choice in the presence of two clearly 
apprehended alternatives. There lies before the man who 
is out on a walk a fork in the road. Sometimes he will 
thoughtlessly strike out on that path which he has often 
followed, or because he is absorbed in thought he will be 
guided by mere accident. But in the case in which we are 
interested he sees the two roads clearly ; each is inviting, 
and in terms of his experience and training, equally acces- 
sible ; he may even pause a moment and then he turns to 
the left or right. We can explain this turning in a broad, 
loose way by using such phrases as "he decided," "he 
chose," "he selected." The impressive fact about each 
of these phrases is that it brings out the truth that we are 
in the presence of an explanation which includes and in- 
volves personality. We may speak of impulse in an imper- 
sonal way. One is led to do something when he acts under 
the spell of impulse, but one makes the decision himself 
when he chooses his road. 

Behavior of the higher types dependent on ideas. The 
broad terms of our explanation do not satisfy the demand 
for a scientific account of the process of choice. We 
must go into greater detail. We can do this in some 
measure by pointing out that bodily activity is related to 


ideas no less than it is to percepts. One thinks of a tall 
object and, as we have seen in an earlier chapter, he tends 
to move his eye and his hand upward. One thinks over 
an offense which has been committed against him and he 
grows red with rage and tense for an attack. Ideas are 
related to actions because the nervous processes involved 
in the formation of ideas are, like all nervous processes, 
parts of a succession of processes leading to a motor dis- 
charge. In the association areas of the cerebrum there 
are complex nervous combinations and deposits of earlier 
excitations which are the immediate conditions of ideation 
and at the same time links in the chain of processes 
connecting the sense organs with the motor centers. 

When as a result of experience an individual becomes 
mature enough so that his sensory impulses are taken up 
into -a highly developed train of cerebral processes before 
they are allowed to go to the motor centers, we say of the 
individual that he acts on the basis of ideas. We mean by 
this statement that the instinctive tracts are relatively less 
and less important in this individual's life. We mean that 
the inner organization is more and more important. The 
inner organization of the cerebrum is, as we have seen, 
relatively remote from mere sensation. Hence, when the 
inner processes come more into control we find the expla- 
nation of individual conduct not in present impressions 
but in past experience. The first and most evident con- 
clusion about voluntary choice is therefore that it depends 
on a high development of central paths and is related to 
the higher conscious processes. 

Voluntary action and its complex background as contrasted 
with lower forms of behavior. The significance of the fore- 
going conclusion will be fully grasped only when it is re- 
called that the central or ideational conscious processes are 
complex as contrasted with mere perceptions and other 
conscious processes which involve only the lower elements 


of the nervous system and the lower phases of experience. 
An idea is a composite of experience. The general fact 
about ideational consciousness is that it brings into a single 
instant of experience a vast variety of elements. Conduct 
which is based on ideation is, accordingly, conduct which 
springs, not out of some simple single impression, but out 
of a combination of manifold impressions. 

We have commented in earlier chapters on the advantage 
which comes to the individual from the possession of a 
world of ideas in which the whole of experience can be 
compactly represented and readily rearranged. We see flow 
the advantage to conduct of ideational powers. The indi- 
vidual who has ideas can act on a broader basis than can 
the victim of mere impulse, or the undeveloped individual 
who has only the most immediate sensory motives for his 
comings and goings. 

Decision a process of balancing ideas. Let us consider 
once more our individual who must choose at the fork of the 
road which branch he will follow. No outsider can fathom 
his choice. The inner world is the scene of a balancing 
and comparing, and out of this inner world comes a decision 
which turns the scale of muscular tension and results in a 
movement. If at the moment before decision an outsider 
would influence choice, he must appeal to the inner world ; 
he must reach the thought process of the individual who 
is deciding. 

Decision largely influenced by organization built out of past 
experiences. When we trace decision back into the inner 
world, we find justification for a second general conclusion. 
Volition is determined in very large measure by past experi- 
ences. All ideas, as we know, are explicable only in terms of 
organizations of experience which have been set up in the past. 
The choice which an individual makes to-day has its roots in 
the experiences of yesterday and of the earlier education be- 
fore yesterday. To be sure, the present may bring into the 


mind a manifold of experiences out of which choice must 
issue, but this manifold will be arranged and organized in 
terms which comport with the past as well as with the present. 
We know in ordinary life that it is safe to assume that an 
individual who has made his decisions thus and so in the past 
will in the future exhibit like tendencies of choice. 

The relation of choice to past experience is impressively 
illustrated by the fact that voluntary attention is controlled 
by what one has learned to think about. If one puts oneself 
through a seriqs of experiences in which aesthetical objects 
are again and again examined and recorded in thought, it is 
safe to predict that aesthetic objects will in the future be centers 
of long concentrated attention. If one gives heed for years 
to matters of business to the exclusion of all other objects of 
thought, it is sure to be a great deal easier to fix attention on 
matters of this type in all future experience. 

We come back to the formula with which our explanation 
began. Whatever enters into the personality of a man enters 
into his voluntary choice. When a man chooses, he expresses 
his personality. This is the essential fact about volition ; choice 
is not an arbitrary, sudden mode of thought or action ; it is, 
rather, the consummate expression of all that has entered 
into individual life. 

The meaning of prevision. While emphasizing the impor- 
tance of past experience in the development of voluntary con- 
trol it is important that we should understand also the fact 
that volition looks by means of imagination into the future. 
One recombines ideas and foresees in this world of ideas 
certain consequences of this or that combination. Behavior 
is then dominated, not by present impressions or by habits 
alone, it is guided by the products of imagination. The thinker 
has tried out consequences in the world of thought and has 
the advantage in conduct of these purely mental trials. The 
power of imagination thus comes to be more important for 
human conduct than even habit or instinct. 


For example, the general plans his movements with a map 
before him and with a thousand items of information in mind 
about the enemy and his own forces. His final orders are the 
results of his comparisons and mental experiments. 

The power of choice becomes thus a matter of the relation 
of complex ideational processes to behavior. Conduct is re- 
lated to ideas, and any elaborate process of combining ideas 
which results in a new idea will influence behavior. 

The problem of the freedom of the will. We are now in 
a position to consider one of the problems which has long 
been a subject of hot debate among students of human life 
and conduct ; namely, the problem of the freedom of the will. 
It has been argued on the one side that in a given emergency 
an individual can follow any one of the various courses which 
lie before him. The five or six paths which he might follow 
all attract him, but he is free to follow the one which he 
chooses. So far we must agree. But the extremists seem to 
argue at times that the chooser is in no wise bound even by 
his own earlier experiences and training. The individual is 
free in the absolute sense, we are sometimes told. He may 
at this given moment strike out without reference to his past 
or to any other cause. His action is without determining 
cause. He is a wholly independent being, unguided by any 
outer or inner considerations except as he is willing in his 
sovereign independence to give heed to these considerations. 
This last statement of the doctrine has sometimes been called 
the doctrine of libertarianism. For this view there is no evi- 
dence. Personality is never free from its own past, even when 
it is producing new combinations of ideas through imagination. 
Personality is a product of organization. Personality is the 
name of that individual nature which has been developed out 
of the play and interplay of impressions and instincts and 
conscious comparisons and imaginations. Personality is never 
free from itself. Voluntary choice is an expression of per- 
sonality, not of sheer caprice. 


Voluntary choice guided by purposes. The conclusion 
to which we are thus led gives the largest emphasis to those 
reorganizations of experience which were discussed in the 
chapter on concepts. We saw in that chapter how a dominant 
inner purpose may control the organization of all thought. 
I may resolve to think about a geometrical proposition, and 
all my ideational processes will be rearranged and worked out 
in conformity with this central purpose. The rise in the mind 
of a dominant idea is therefore an important event, not merely 
in a vague, abstract sense, but in a practical sense as well. 
When some personality takes up with fixed purpose a definite 
line of thought, his own conduct and ultimately that of his 
social environment will be affected. This is what was meant 
by the statement that consciousness is a cause and a very 
potent cause in the world of affairs. 

Behavior of a higher type is related to education. A text- 
book on the science of human mental processes is not the 
place for a homily on conduct, but it is so obvious an in- 
ference from what has been said that one can hardly refrain 
from recording the principle that all choice and all signifi- 
cant human influence in the world are dependent for their 
character on the growth of ideas. He who would influence 
his own conduct or that of others must therefore look to 
the roots of conduct in organized processes of ideation and 

It will be proper, therefore, for us to follow the study of 
voluntary behavior by a discussion of some of the more 
obvious devices by which human choices may be turned in 
the direction of fruitful and efficient developments. 

Early scientific studies of behavior purely external. Before 
we apply the lessons we have learned, we owe it to the his- 
tory of scientific method to comment briefly on the develop- 
ment of scientific studies of human behavior. The earliest 
scientific investigations of bodily activities were undertaken 
from a wholly external point of view. The specific method 


which was used for such investigations was devised by the 
astronomers who were interested in understanding the defi- 
ciencies of human movements when attempts were made to 
use these movements in recording the transit of stars through 
the field of the telescope. The astronomers found that the 
hand cannot be moved as soon as the eye sees a light. 
They therefore measured the interval which elapsed between 
visual impression and hand movement. They found further 
that different individuals have different personal equations, 
or periods of reaction. Evidently the observations of the as- 
tronomers are very suggestive as foundations for psychological 
investigations. The early psychological investigators, how- 
ever, did not transform the method into a psychological 
method ; they took it over unmodified. Their investigations 
of the active processes were not based upon any elaborate 
analysis. Certain simple movements were measured with 
reference to the time which elapsed between the stimulus 
and the muscular contraction, exactly as this time had been 
measured by the astronomers. The investigation of this time 
of reaction was treated as an indirect means of getting at the 
complexity of the nervous and conscious processes preceding 
the reaction. It was found, for example, that the length of 
time required for a simple reaction was appreciably shorter 
than the length of time required for a reaction which involved 
the discrimination of two simple colors from each other. Thus, 
if the reactor were required to move his finger as soon as 
possible after being stimulated by a flash of light, the meas- 
urement of this interval gave what was called a simple reac- 
tion time of about -ffifa of a second, or i8o<r, the letter <r 
being used as the symbol for a thousandth of a second. If, 
on the other hand, the experiment was arranged in such a 
way that a number of different colors could be presented to 
the subject, and it was prescribed that he should react only 
after a clear recognition of one of these colors, then the clear 
recognition or discrimination added appreciably to the time 


which elapsed between the giving of the stimulus and the 
movement, sometimes as much as 60 <r. This longer period 
of time was known as discrimination time. Again, if instead 
of reacting always with the same hand or finger the reactor 
was instructed to respond to one kind of stimulation with one 
movement and to another kind of stimulation with a second 
movement, the process involved not merely discrimination 
but also a simple choice of the organ to be moved. The 
reaction time in this case was called choice time. 

Purely external investigations not productive. The earlier 
experimenters on reaction were satisfied to seek exact defi- 
nitions of the lengths of these various kinds of reaction 
time. They paid little or no attention to introspection on 
the part of the reactor. The results of a large number of 
reactions were averaged, and the comparison between differ- 
ent simple mental processes was made in terms of these 
general averages. The outcome for psychology of these ex- 
ternal studies was by no means large. There is very little 
contribution to the knowledge of human nature in the details 
of reaction times. 

Recent investigations and their stress on introspection and 
analysis of movement. Recent investigations of reactions 
differ from the earlier external measurements in two re- 
spects. First, the effort has been made to find out, as far 
as possible, what are the conditions in the experience of 
the reactor during the reaction process. Attention has been 
called, for example, to the fact that if the reactor's atten- 
tion is turned toward his hand, rather than toward the organ 
of sense which is to be stimulated, the time of reaction will 
for most individuals be shorter. A distinction may therefore 
be drawn between so-called muscular reactions and sensory 
reactions. The average difference in time corresponding to 
this introspective difference is often as great as ioo<r. Again, 
the different types of discrimination and choice have been 
introspectively examined. The question of whether the 


content of consciousness before a choice reaction is an image 
of the movement to be executed, or a concentration of atten- 
tion upon the sensation received, has been introspectively 
studied. The results of these introspective studies have done 
much to clear up the psychological doctrine of volition. Fur- 
thermore, the general outcome of a more careful examina- 
tion of conscious correlates of reaction has shown how utterly 
formal was the gross averaging of all kinds of cases in the 
earlier investigations. It may be said that no introspective 
differences ever occur without some modification in the dura- 
tion of the reaction process ; hence, differences in duration 
are highly significant when supported by introspective ob- 
servation and should not be eliminated by an arbitrary 
method of mathematical averaging. 

Analysis of the form of movement. The second way in 
which recent reaction experiments have been elaborated is 
by analyzing the forms of the reaction movement. It was 
formerly assumed that the act of lifting the hand from a 
reaction key was so simple a process that it could be re- 
garded as uniform in character throughout a long series of 
experiments. Recent investigations show that there is no 
such thing as an absolutely uniform series of movement proc- 
esses. There are certain reactors, for example, who, when 
they make an effort to lift the hand as rapidly as possible, 
frequently go through a preliminary downward movement 
before beginning the upward movement. There are other 
preliminary phases of movement which prepare the way for 
the final reaction, and the relation between these preliminary 
movements and the final movement of the hand may be so 
complicated as to influence measurably the duration of the 
reaction period. The relation of these complexities of move- 
ment to nervous organization is most intimate. The studies 
in earlier chapters of the relation of perception and feeling 
to reaction have indicated the significance for psychology 
of the analysis of reactions. By way of criticism of the 


earlier studies, it may be said that they treated reactions as if 
they were merely uniform mechanical processes. The recent 
investigations have made it clear that the study of muscular 
behavior is productive only when it is related to a complete 
account of the introspective processes and the antecedent or- 
ganizations which condition the particular form of movement. 
Concept of organization as fundamental in all psychologi- 
cal studies. The study of movement has therefore brought 
us back to the consideration of principles of organization. 
Volition and impulse are merely the active correlates of or- 
ganized forms of ideational and perceptual experience. The 
earlier studies of mental activity and the present study of 
behavior are mutually supplementary. We do not require 
any unique formulas or the recognition of any new factors. 
Behavior is a necessary and ever-present physical correlate 
of experience and, at the same time, a product of all those 
organizations which lie back of experience itself. 



Hygiene a suggestive tern* for psychology. Just as there 
is a way of keeping one's physical organs in good condition 
through the adoption of rational principles of nutrition and 
exercise and sleep, so there is a way of organizing one's 
mental processes with a view to meeting most efficiently the 
demands of life. 

Relation of psychological hygiene to physiological. The 
first maxim of mental hygiene is that the nervous system 
must be kept in a healthy condition. Indeed, physical hy- 
giene here becomes an essential part of the application of 
psychology. If the nutrition of the body is defective, the 
nervous system suffers with the other organs, and the mental 
processes become abnormal. The same is true of sleep and 
the excretory processes. The body must be in good condition 
if the mind is to do its work. 

Coordination of bodily activities. Assuming for the pur- 
poses of our discussion that the general physiological condi- 
tion is favorable, the next maxim of mental hygiene is that 
all one's activities must be brought into harmonious coopera- 
tion, for the first function of the central nervous system is 
to control and coordinate the parts of the body. Thus, when 
muscles are contracting vigorously, there is a call for blood 
in the particular part of the body which is in action. The 
nervous system must distribute the blood supply of the body 
in such a way as to meet the strenuous local demand and at 
the same time keep all of the supporting organs properly 
supplied. The young child has to acquire the ability to do 


this. At first his organic activities are subject to all kinds 
of distractions and incoordinations. He is unprepared for any 
sustained effort because his body is not yet a well-coordinated 

Perhaps the most striking illustration of the incoordina- 
tion of a child's body is seen in the fact that excitement of 
any kind interferes with digestion. Digestion is in very 
large measure an active process. The glands are active in 
secretion, and the muscles of the digestive organs contract 
in rhythmical movements that are necessary in carrying the 
food through the alimentary tract. The elaborate system of 
organs thus involved in digestion must cooperate or the whole 
process will be disturbed. Suppose that all is going well, 
when suddenly a shock of violent stimulation comes to the 
nervous system. The flood of uncontrolled excitement will 
be discharged by the motor fibers into the inner muscular 
system, and digestion and circulation and respiration will 
be violently disturbed. It is one of the important results 
of training that disturbances of this type are overcome in 
increasing measure. The mature nervous system tends to 
check and distribute excitements so that the organism may 
not be disturbed in its fundamental activities. 

Little children are very often disturbed by mere social 
excitements to an extent which seriously interferes with 
life. An adult, on the other hand, can receive the same 
kind and amount of stimulation and not be distracted from 
the inner activities of organic life. The training of one- 
self to receive all sorts of external stimulations without dis- 
locating the inner machinery is one of the important lines 
of personal training. 

Control of excessive stimulations. The formulas which 
can be adopted for such training are apparently contradic- 
tory. First, one should have regular habits of life. This 
will set up wholesome and balanced forms of action. 
Second, one should expose himself from time to time to 


irregular and exciting situations. Or, perhaps better put, one 
is sure, if he lives in the world with its various kinds of 
experience, to be drawn out of mere routine by forms of 
excitement which tend to break up his simple habits of life. 
Then one should aim to overcome the disturbance of Inner 
life by deliberately controlling the excitement in order to 
give the organic habits an opportunity to reassert them- 
selves. Control often means relaxation. Let an excited 
person take two or three long breaths ; let him relax the 
jaw muscles or the muscles of the hands. Excitement which 
tightens up the muscles can often be overcome by these 
sheer physical devices. If the physical devices do not 
suffice, let there be an appeal to voluntary effort. If the 
excitement is one of fear, let the excited person face the 
problem and explore the source of the fear. Let one reason 
himself, if he can, into a less tense attitude. The fact is 
that every experienced adult has in the course of his life 
come to the point where he can deal more or less success- 
fully with excitement. Ability to master excitement shows 
an internal state of coordination of a high type. The organ- 
ism has acquired ability to undertake several kinds of action 
at once without interfering with its own life. 

While emphasizing the importance of internal harmony, 
it may be well to refer once more to the disintegrating 
effects which follow chronic incoordination. All the disso- 
ciations which were discussed in an earlier chapter have in 
them elements of internal discord. The individual whose 
nervous system is sending out conflicting and discordant 
impulses is an unhappy individual in his conscious experi- 
ence and an incoordinated individual in his active life. 

Perceptual analysis. A third maxim of mental hygiene is 
one which relates to perception. All progress in perception 
and in muscular coordination results from particularization 
or concentration of attention on definite items of experience. 
It is worth the effort for everyone to learn to analyze the 


objects in his environment. Even if one is not going to use 
the details of information at the moment, it is valuable from 
the point of view of future adaptation to be able to concen- 
trate attention and action on particular aspects of a situa- 
tion. Most games illustrate this kind of demand. If a boy 
learns to catch a ball, he trains himself in concentration of 
attention and control of his muscles. In the animal world 
nature provides young animals with a play impulse through 
which the untrained individual is led into exploratory forms 
of behavior which in later life will be of use in nosing out 
real enemies and real prey. 

As a practical measure of self-training, it may be urged 
that everyone ought always to analyze what he encounters. 
He should notice the details of behavior of those whom he 
meets ; he should note the contour of the objects he sees. 
If he gets a hint that there are details which he has over- 
looked, let him train himself to go back and find these 
details. The value of such self-control is not merely in the 
results gained at the moment, but in the conscious tendency 
to analyze. It was pointed out in an earlier chapter that 
perception is an active process initiated by the individual. 
The application of that lesson is that the individual must 
be active if he would perceive completely. 

Perceptual synthesis. The counterpart of the foregoing 
demand for analysis is the demand that one cultivate the 
power of grasping many impressions at the same time. The 
observer should train himself to recognize at a glance as 
much as possible. It is said that the schools which train 
performers to give exhibitions of ability to recall a whole 
box full of trinkets after a single glance begin in childhood 
by exposing to the prospective performer for recognition, 
after a very brief exposure, three objects, then four, then 
five, and so on. The scope of attention is thus broadened. 

All forms of expert observation involve this breadth of 
apprehension. The expertness cultivated in reading involves 


the power of recognizing at a glance a series of words. The 
child is limited in his ability to grasp words and only gradu- 
ally reaches the stage where he can take in many at once. 
The poor reader is found to be one who has made little 
progress in the cultivation of a broad range of attention. 
Many an adult is seriously handicapped because he can 
recognize at a glance only one word. The individual who 
finds himself thus limited should train himself by going 
rapidly over familiar material. The familiarity will give the 
necessary clearness to details, for familiarity is likely to im- 
ply some earlier analysis. The rapid view of the familiar 
material will help to synthesize many elements into a single 
experience. The limits to which skill may be cultivated in 
this matter are described by saying that an expert reader 
can very often surpass by two or three hundred per cent 
an ordinary reader. 

What is true of reading is true of other situations in 
which expertness can be cultivated. The person who draws 
learns not only to see minutely but to take in the totality 
of a situation. The architect sees many features of a build- 
ing and shows a grasp of both detail and general appear- 
ance which the untrained individual can hardly compre- 
hend. The skilled artisan sees more in every piece of 
work of the type which he knows than can an inexpert 

Dangers of specialization. There appears at this point 
one of the crucial difficulties in education. Perception is a 
process in which individual development is often highly 
specialized. For example, the skilled artisan may see much 
in the kind of materials with which he is used to dealing 
and be quite oblivious to other perceptual facts ; the shoe- 
maker sees the shoes which a passerby wears, but has no 
interest in his tailoring. The fact is that perception is closely 
related, as was shown in an earlier chapter, to special train- 
ing in direct manipulation. The extension of experience to 


include many different kinds of percepts will therefore re- 
quire deliberate effort on the part of the observer; other- 
wise he will fall into narrow modes of seeing only a small 
part of the world. 

Control of perceptual attitudes. Not only so, but the 
limited range of ordinary perceptual experience is exhibited 
in the fact that our attitudes toward the objects about us 
are very often quite irrational. One dislikes a person whom 
one meets, for no better reason than that the stranger re- 
sembles an acquaintance whom the observer does not like. 
The child likes a color because he saw it first in an agree- 
able setting. If experience takes its course without super- 
vision, these attitudes become fixed and the narrowness of 
perceptual interpretation passes into a lifelong habit. 

Practical study of one's own attitudes ought to raise one 
above the level of accidental attitudes. It often requires 
time and effort to set aside one of the ready-made reactions 
which so easily attach to percepts. The person who is afraid 
of thunder and lightning may have to drill himself for years 
to overcome this attitude which has become second nature, 
but a new attitude can be cultivated by anyone who will set 
himself to the task. 

Control of attitudes as a case of volition. In general, the 
types of training which have been advocated in the last two 
paragraphs are types which can be accomplished only through 
the domination of experience by higher mental processes. 
A man must know something of himself in an ideational way 
if he is deliberately to cultivate new ranges of perception and 
new attitudes. What he accomplishes through self-control 
will ultimately reach back into his perceptual life and will 
make him alert about many new opportunities to see and 
hear; it will also make his -personal attitudes more rational. 
The result will be a richer perceptual life and a more whole- 
some series of attitudes. Perception will thus grow and 
overcome the inherent tendency toward specialization. 


Rules of wholesome ideation. When one comes to 
memory and ideation, to language and abstraction, the field 
of applications in personal life is unbounded. A few par- 
ticular maxims of mental hygiene in these fields may be 
selected, but the student will have to supply for his own case 
most of the rules which will insure success of his mental 

Economy of mental effort. One of the special problems 
of memory is the problem of economy of effort. If one has 
a passage of prose to learn by heart, how should he do it 
by learning a line at a time or by taking in large units ? 
The answer supplied by careful experimentation is that he 
should learn by large units. The reason why learning by 
large units is advantageous is not far to seek. If one reads 
to the end of a line and then goes back to the beginning of 
the line, he sets up an association between the two ends of 
the same line, whereas he ought to set up an association 
between the end of the first line and the beginning of 
the next. 

The maxim that one should learn by large units can be 
amplified to include many cognate cases. The student trans- 
lating a foreign word looks up the word in the vocabulary 
and glances through a long list of meanings, most of which 
he rejects. It would be economy of mental effort in the 
long run if he would master all the meanings, rejecting none 
but including all in a complete view of the word. The failure 
of the student to see this is due to the apparent ease of 
accomplishing the limited immediate purpose, whereas he 
ought to cultivate a broad, though more remote, purpose. 

Preparation as aid to memory. Another general principle 
of memory is that even a very abstract scheme which pre- 
pares the mind in advance to retain experiences will make 
it possible to hold more in memory than can be taken in 
if the material is not arranged. This is illustrated by the 
man who prepared himself to remember long arbitrary lists 


of words by setting up in his mind a series of a hundred 
rooms, arranged in fixed order, in each of which was hung 
a single mental picture ; then when the words to be re- 
membered were given, he associated one with each succes- 
sive mental room and picture. Later, by going through the 
rooms in order, he could recall the series of associated 
ideas. The prearranged mental scheme was the key to his 
power to retain. 

Still better is a rational scheme. The student of science 
gets ultimately an outline of his subject in mind, and every 
new author whom he reads falls into this scheme and is 
classified in detail. A trained student thus cultivates a 
method of remembering a great body of opinion by classi- 
fying it. 

If one wants to learn to remember what cards have been 
played in a card game, let him have a plan of arranging 
his own hand, and then the accidents of the game will be 
forced into an orderly scheme. 

Organization the key to all correct thought. The general 
formula which emerges from all these examples is the 
formula of organization. Ideas should be arranged. When 
ideas are arranged, they can be carried in greater bulk 
than when they arc isolated. Indeed, they can never be 
isolated in any absolute sense because some kind of asso- 
ciation will always couple them together. Arrangement 
means, therefore, an association which is dominated by 
some clear purpose or plan. 

The domination of thought by some leading idea. This 
general formula can be employed also in treating briefly 
some of the phases of abstraction. The world is for each 
individual rearranged in terms of personal interests and 
personal modes of abstraction. The man whose ambition 
is wealth selects out of everything that comes into his 
experience those elements which have to do with money. 
He comes ultimately to see the world from the one point 


of view. The man whose ambition is power sees men and 
things from an entirely different point of view. The man 
without ambition drifts about, looking at his world to-day 
from one point of view, to-morrow from another. Abstrac- 
tion is the most subtle and pervasive fact in individual life. 
We all transform the worlds in which we live by the pur- 
poses which control us in life. So absorbed do we become 
in our personal points of view that it requires a serious jolt 
to bring us back to the point where we are willing to make 

Language of great importance in furnishing central ideas. 
The importance of language as an instrument of social ab- 
straction will be instantly recognized in the light of what 
has gone before. There are phrases current in language 
which dominate personal thought and make our thinking 
like that of our neighbors. Take such a word as "effi- 
ciency " ; the world is different to a man after he acquires 
that word as a part of his working vocabulary. 

The ineffectiveness of a detached verbal idea. The mean- 
ing of these statements for individual development can 
hardly be misunderstood. The practices of the schools in 
making language subjects the center of the course of study 
can be defended in the light of a psychological study of 
language. To be sure there is danger in mere verbal 
reactions. Language subjects in the schools need to be 
brought back into relation with the practical activities of 
life in order to insure the use of words as instruments 
of real abstraction and social intercourse. Mere words may 
be trivial, but words as guides to thought and as instru- 
ments for the determination of abstractions are powerful 
factors in controlling personal thought and action. 

To the student who spends most of his time dealing 
with books perhaps the warning in the last paragraph 
should be made somewhat clearer. The cerebrum is so 
complex in its structure that a tract may be established 


through its tissue, leading from the visual center directly 
to the speech center. Words read will be repeated, but if 
this short circuit alone is set in action, the process will 
have to be described as one of mere repetition. 

Higher organization as a cure for verbalism. The remedy 
for mere verbalism is the development of larger systems of 
behavior. The eye may see a long stick and the hand 
may use this stick under the guidance of organized experi- 
ence to pry up a weight. This reaction with the stick may 
not arouse at all the speech tract above described, even 
though the speech tract has been aroused by a textbook 
in physics to repeat a passage about a lever. The indi- 
vidual thus contains within his complex life one series 
which is a series of reactions with a real lever and another 
series which tells about levers. There is a possibility that 
these two tracts existing side by side will not affect each 
other in any way. The individual who is aware of this 
dangerous type of separation of relatable activities within 
himself will make a conscious effort to unite verbal reac- 
tions with practical reactions. He will aim to set up a 
higher internal organization including both speech and 
hand adjustment. 

A neglect of this demand for complete internal develop- 
ment is one of the most serious dangers of our present-day 
education. The real trouble is not that words in themselves 
are bad or that handwork in itself is limited, but in the 
rush of modern life the two are cultivated side by side and 
neither gets the benefit of the other. What is needed is 
a higher type of organization which will include the ver- 
bal or theoretical discussion of levers and the illuminating 
experiences that come from having levers in the hand. 
This higher form of experience will bring to practical life 
all the advantages of abstraction and to abstract life all 
the advantages of concrete application. Both ends can be 
reached in one and the same individual. 


Self -directed organization as the goal of the higher mental 
life. Again we find ourselves speaking in terms of higher 
forms of organization. Wherever the individual can compre- 
hend in a single system of nervous or mental organization 
more elements, there the adaptations of life and experience 
will be broader and better. The lesson is clear. The indi- 
vidual must seek of his own initiative those higher forms 
of organization which will realize most fully the possibilities 
of his life. 

The highest level of individual organization is reached 
when mental development becomes a matter of voluntary 
control. Under the definition of volition which was worked 
out in the last chapter it was seen that volition consists in 
a control of action through intellectual prevision of results. 
So it is also in the mental world. When the mind by self- 
study sees the goal which self-development should reach, 
it is possible by voluntary effort to move toward this goal. 
Thus we have seen how knowledge of the nature of per- 
ceptual attitudes may guide one in modifying these atti- 
tudes. In like fashion, knowledge of the limitations of 
study of theory may guide one in cultivating applications. 
Knowledge of one's own limitations may lead to a per- 
sistent attack upon these limitations. In short, voluntary 
self-development means the cultivation of the broadest 
possible systems of behavior. 



Psychology a basis of scientific thinking about human 
conduct. There are many phases of practical and scientific 
thought regarding human activity which are illuminated by 
the study of psychology. Indeed, wherever human nature is 
a factor in any set of phenomena, there is need of a clear 
understanding of the human contribution to the situation, 
and this can be supplied in scientific form only by a study 
of psychology. The complete demonstration of the useful- 
ness of psychology would require a series of supplementary 
chapters. It will be enough for our present purposes if the 
general outlines of some of these discussions are presented. 

Design in art as a psychological fact. Our first illustration 
can be drawn from the field of the fine arts. This is a sphere 
in which the relations of the individual to his external en- 
vironment are relatively free. When the artist paints a pic- 
ture, he is guided, so far as the design of his production is 
concerned, by the laws of his own taste. Art grows out of 
the demand for subjective satisfactions, not out of any com- 
pulsion imposed by the physical world. It is for this reason 
that psychology draws many of its best illustrations from the 
sphere of art. If we find a general principle running through 
art, we are led at once to the conclusion that there is a cor- 
responding tendency in human nature. Certain simple illus- 
trations may be offered. Thus, there is a certain proportion 
between the long and short sides of rectangular figures which 
is pleasant to look at. The proportion can be expressed mathe- 
matically by saying that the long side is to the short side as 



the sum of both is to the long side. If we examine those 
objects which have been freely constructed without special 
external limitations, we shall find that a great many of them 
take on this proportion. For example, when an extensive 
series of measurements was made of the two legs of orna- 
mental crosses, it was found that they maintain the propor- 
tion described. This fact can have no objective explanation 
and must have been dictated by human subjective attitudes. 
Freedom in art. Again, certain of the types of sym- 
metry in architecture are efforts to meet the demands of 
human nature rather than of external requirements. If we 
examine the forms of architecture which grew up in a period 
when men were free, so far as the external environment was 
concerned, to construct buildings of any size which they 
pleased, rather than to fit their constructions to the require- 
ments of a qity building lot, we find that the size and form 
of these free buildings assumed certain general proportions 
which were determined, not by the external conditions, but 
rather by the demands of taste. Indeed, one of the funda- 
mental distinctions between ancient and modern architecture 
is a distinction which can be described by saying that the 
early builders followed their sense of proportion, while modern 
builders follow certain definite laws of mechanical construc- 
tion. A Gothic cathedral of the pure type very commonly 
exhibits certain irregularities in the position and size of its 
columns, which yield in the mass an impression of solidity 
and symmetry that could not be obtained if every part of the 
building had been made to conform to exact mechanical rules. 
A modern building is constructed with definite reference to 
mathematical regularity of dimensions and with reference 
also to the strain which is to be placed upon every given 
part of its floors and walls. There is little tendency to 
use the material freely; there is much greater tendency to do 
only what is necessary to meet the simpler mechanical re- 
quirements. A column made of steel is designed to support 


a certain weight, and the size of the column used in a build- 
ing is usually determined by the weight which it is to carry 
rather than by its appearance. The immediate effect of at- 
tention to such mechanical requirements is that we have 
many ugly buildings. 

Architectural harmony analogous to musical rhythm and 
harmony. There are many indications in the earlier, freer 
architecture of the Greeks that they followed certain broad 
principles of rhythmical proportion which correspond so closely 
to what we find to be the principles of musical rhythm and 
harmony, that there is a suggestion of a common type of 
human organization lying back of both spheres of art. It has 
been pointed out, for example, that the height of a Greek 
column is an exact multiple of its diameter. Furthermore, the 
space between the columns always stands in definite relation 
to the diameter of the column. In details of construction 
also, as, for example, in the various portions of the decora- 
tions in the Ionic capital, the parts are related to each other 
in definite unit ratios, so that a constructive symmetry runs 
through the whole and gives the observer a feeling of com- 
posure and unity. 

Literary art and psychological laws. What is true of 
architecture is much more obvious with reference to literary 
art. It is clear that the laws of literary composition must be 
laws of human nature, and the great artists have unquestion- 
ably followed with sufficient closeness the demands of human 
nature to leave their works as standards for future develop- 
ment and as expressions of the direction in which all individual 
development must tend. 

Prose rhythms as related to the personal organization of 
writers. Some purely formal indications of the complete- 
ness with which great literature conforms to the demands of 
human nature may be found in the fact that there are even 
in prose compositions certain typical rhythms which give to 
these compositions a regular symmetry of character, which 


undoubtedly constitutes one of its charms. It is a striking 
example of the fact that art may outstrip science, that it is 
not yet possible to give any complete theoretical account of 
the prose rhythms of the best writers. Evidently those who 
have contributed the great works to literature have succeeded 
in utilizing the language in which they wrote in such a way 
as to express an internal organization of their own which was 
altogether appropriate to their theme and to the vernacular, 
and this they have done spontaneously and very often without 
complete theoretical recognition of what they were doing. 
When the student of such prose arrives by laborious analysis 
at some knowledge of the rhythms which it contains, he is 
not creating rhythms, but rather rediscovering by the tardy 
methods of scientific analysis a formula which has been 
achieved by the great writer through intuition. 

Verse another example of the same type. If the forms 
of prose composition have exhibited complexity of structure, 
together with a fundamental regularity of form, it is even 
more true of verse that its masters have never followed rigid 
mechanical principles in their work. And yet they have ade- 
quately met the demands of human nature. Their conformity 
to a limited group of principles is seen in their adherence to 
certain regular forms which are sufficiently obvious to be imi- 
tated in gross outline by writers of less taste and power ; but 
the full and effective use of verse forms has always involved 
a certain freedom of manipulation which has defied any com- 
plete theoretical account. Psychology must frankly admit in 
such a case as this that it follows in the steps of a complete 
adaptation, very far behind the adaptation itself. Neverthe- 
less, the psychological problem is clear, and a general sug- 
gestion as to the explanation of these facts may be found in 
what has been said in an earlier connection regarding the 
nature of rhythm. Whatever the unknown details, rhythm 
is certainly in keeping with the natural demands of the nerv- 
ous system. Because the nervous system is rhythmical in a 


complex way in its own functioning, it responds favorably to 
rhythms of impressions. 

Literary content controlled by psychological laws. It is 

not alone in its form that literature expresses the demands 
of human nature ; the content may be studied from the same 
point of view. It is possible by a psychological analysis to 
throw much light on one case which has been the subject of 
much mystical speculation. It has often been suggested that 
human intuitions and vague feelings frequently bring us much 
nearer to that which afterward proves to be the truth than do 
oiir most elaborate processes of reasoning. The poet has 
always claimed for himself a higher position than he would 
allow to the scientist who is bound by the demands of rigid 
evidence. We often speak of the insights of the artist, and 
mean by this phrase that the artist sees beyond the ordinary 
facts of definite observation and clear vision to ranges of facts 
which are of importance, but are not open to our inspection. 
Feeling and intuition. What has been said in an earlier 
chapter with regard to the nature of feelings will be of some 
assistance in clearing up the paradox which here appears. 
When explaining the feelings, we discovered that whatever 
runs counter to the organized nature of the individual will 
arouse a disagreeable feeling. Whatever is in fundamental 
agreement with nature will give pleasure. If now the ex- 
periences of life are in subtle agreement or disagreement 
with the organization of the individual, it does not follow 
that the individual will become clearly conscious of this fact 
in ideational or abstract terms, and yet he may be vividly 
aware of the disagreeable feeling imposed upon him by a 
certain experience. For example, as we have seen in earlier 
discussions, the organization of an animal may be such that 
certain color stimulations are fundamentally opposed to its 
natural organization. Feeling is, therefore, a kind of spon- 
taneous adjustment with a practical value which often sur- 
passes that of incomplete theoretical judgments. Feeling 


may be relied upon in those situations where the organiza- 
tion is simple enough or the response direct enough to 
give an unbiased reflection of the individual's relation to the 
impression. On the other hand, when life becomes complex, 
as it is in human beings, native instincts and native feelings 
are often overlaid by a series of developments so indirect 
that there comes to be a certain rivalry between the author- 
ity of feeling and the authority of abstract knowledge. 
There can be no doubt, for example, that the social selec- 
tions by which one determines who shall be his friends are 
dependent in large measure on intuitions, but one does not 
need to be very old or worldly-wise to recognize that the 
complexities of social life are such that the instinctive feel- 
ings which we have in making the acquaintance of new 
individuals are not always safe guides in the development 
of social relations. What is true of social relations is true, 
undoubtedly, of artistic intuitions and of larger intuitions of 
universal truth. It is quite impossible to persuade one who 
regards a line of poetry as beautiful that it is not beautiful 
because it violates some rigid law of versification. It is 
quite impossible to convince one who enjoys a certain pic- 
ture that the picture is deficient because it does not comply 
with certain canons of a certain school of art. On the other 
hand, it is frequently possible, by a series of educative con- 
tacts with better artistic and literary forms, gradually to 
modify an individual's organized feelings so that he shall 
completely change the character of his judgment. Intuition 
is, therefore, not a separate and distinct faculty of life ; it is 
rather an expression of that immediate form of recognition 
of congruity or incongruity which characterizes the feelings 
as distinguished from abstract theoretical knowledge. The 
statement made by the poet may express an attitude which 
is true to the facts and will later be fully explicated by the 
clearer ideational view 'cultivated in abstract thought. There 
is no ultimate opposition between feeling and thought. 


Many of the social sciences predominantly objective in 
their methods. When we turn from the discussion of art 
and feeling to certain more practical spheres of investigation 
involving human nature, namely, those taken up in the 
social sciences and anthropology, we find that the study of 
psychology is very direct in its application to these spheres 
of study and explanation. It has not always been fully 
recognized that psychology has a relation to the social 
sciences. Certain schools of social scientists have treated 
the institutions which they study merely as objective facts. 
To show this, we may take as an illustration one of the 
oldest of social sciences ; namely, the science which deals 
with language. Language is a product of human activity 
which has a sufficiently independent existence to make it 
an easy subject for examination and analysis. To trace the 
history of a word is to undertake an investigation which 
calls for little reference to the individuals who may have 
made use of this word. In like fashion, the study of a sys- 
tem of sounds and written symbols may result in the dis- 
covery of certain regularities and laws of phonetics without 
reference to the human beings who used this language and 
who were the ultimate sources of regularities in the lan- 
guage itself. The same historical and objective methods 
have been applied to the study of other institutions. For 
example, religious systems have been described and their 
uniformities and divergencies have been ascertained without 
more than a passing reference to the individuals who 
developed these systems or adhered to them. 

Introspective psychology and its limited support to social 
science. The tendency to confine attention to an objective 
study of human institutions has been strengthened by the 
attitude which for a long time prevailed in psychology, when 
the chief method of investigation was the introspective 
method, according to which the individual attempted to dis- 
cover the laws of mental life through an examination of 


his own immediate experience, and with very little refer- 
ence to the modifying influence of his fellow beings or the 
secondary factors of his environment. When the problem 
of psychology is more broadly conceived, so that it is seen 
that the character of human mental life can be defined only 
by a more elaborate study of numerous examples and ex- 
ternal relations, the spheres of institutional study and of 
psychological investigation are gradually brought nearer to 
each other. 

Interrelation of psychology and social science. In the 
course of recent psychological study, much valuable illus- 
trative material has been borrowed from the sciences which 
deal with language and from anthropology. Psychology has 
thus expanded under the influence of the new body of 
material which has been adopted into' it. The methods of 
psychology have become more objective, and the results 
of individual introspection have been broadened. On the 
other hand, the scientific study of all other human beings 
must be based upon one's own personal experiences. One 
naturally thinks of primitive man in terms of his own men- 
tal experiences. If there is no scientific study of the matter, 
the student is likely to carry over analogies and apply them 
to cases where they do not illustrate, but rather obscure, 
the truth. Thus, as has been pointed out by a recent writer, 
there is a widespread tendency to describe the mental abili- 
ties of savages by means of a succession of negatives. Savages 
do not count, they do not have a full series of color terms, 
they do not paint pictures or write. All these negatives 
are mere expressions of the natural tendency to accept our- 
selves as standards. We should become sufficiently imper- 
sonal in our studies to recognize that savages probably have 
a nicety of space perception which is very much greater 
than ours. They may not select color qualities and name 
them, but for the finer grades of variation in plant and 
animal life as indicated by color they have the most highly 


developed discrimination. Not only the savage, but even 
our contemporaries in different civilizations from our own, 
are exceedingly baffling unless we make some study of their 
types of mental development. The institutions of Tibet, 
China, and Japan are obviously different from our own, but 
the character of the mental processes back of these insti- 
tutions has been little thought of and little studied. The 
careful scientific study of the mental characteristics of 
different peoples is one of the most promising lines of 
extension of psychological study. 

v Human evolution psychical. So intimately is social 
organization bound up with the mental development of the 
individual that we are justified in the statement that psychol- 
ogy is the basis of any explanatory account of social insti- 
tutions. There is one particular anthropological problem 
where the significance of psychological analysis can be 
made very clear. Anthropology has never succeeded in 
finding structural modifications in the human body which 
would at all adequately account for the great superiority of 
highly developed races over the more primitive tribes of 
mankind. Even the explanation of the crucial development 
by which man became differentiated from the animals is 
one of the obscure chapters in anthropology. It cannot be 
denied that the explanation of all these matters must be 
sought in terms which refer to the development of intelli- 
gence, especially the development of language and the use 
of tools, as has been indicated in an earlier discussion. 
The problem of anthropology is thus distinguished from 
the purely biological problem, where intelligence is not rec- 
ognized as playing any part. How could a certain group of 
animals suddenly break away from the established type of 
evolution in which changes in structures played a large part 
and become animals characterized by intelligence, meet- 
ing the emergencies of their lives by a mental adaptation 
of themselves rather than by a purely physical adaptation ? 


Why should this group of animals turn to the develop- 
ment of all the instruments of civilization ? The problem 
stated in this form becomes a problem of functional de- 
velopment rather than a problem of physical development. 
This animal must have been driven at some time into a 
situation where his development turned upon his ability 
to adopt a new type of behavior and a new mode of life. 
There can be no doubt that the scientific explanation of 
the breach between man and the animals depends upon 
the recognition of a transformation in the mode of behavior 
and mental life rather than upon any fact of gross bodily 
change. Put in another way, the statement may be made 
that we need no animal form to serve as a connecting 
link between man and the animals. The common struc- 
ture, the common physical needs of man and the animals, 
are now made out so fully that what science requires is an 
explanation of the gap, rather than the link, between man 
and the animals. The doctrine of biological evolution has 
successfully established the principle of continuity. It re- 
mains for genetic psychology to explain the discontinuity 
which appears when intelligence begins to dominate, when 
sensory-motor adjustments of the reflex and instinctive type 
give place to habit acquired through individual intelligence 
and to the more elaborate forms of thought. 

A hypothesis to explain the break between man and 
the animals. An interesting hypothesis has been suggested 
which illustrates the possibility of assuming a distinctly func- 
tional attitude toward the question of the evolution of man. 
This hypothesis suggests that the gradual changes in physi- 
cal organization which characterize all of the different species 
of primates lead up to the appearance of man only because 
at one time a number of these primates were forced, prob- 
ably by the emergencies of a glacial climate in certain quar- 
ters in which they were confined, to adopt a mode of life 
which brought them down out of the trees and forced upon 


them types of activity which led to their construction of arti- 
ficial shelters and to the preparation of forms of food which 
had not been previously utilized by their race. The change 
here assumed depends on the rise of a powerful motive for 
new ways of behavior. Whatever change there was in the 
individual consisted in the opening of new paths in the cen- 
tral nervous system. This change in the trend of evolution, 
when once it appeared, was so important that the further 
history of the group of animals which succeeded in effecting 
it was in the direction of adaptation through intelligence 
and nervous organization rather than through gross changes 
in bodily structures. Whether we give any credence to this 
hypothesis or not, it expresses admirably the functional atti- 
tude in the explanation of human evolution. It expresses 
clearly the fact that the nature of mental and functional 
adaptation is the significant problem for anthropology rather 
than the mere search for changes in physical organization ; 
it gives to anthropology a definite impetus in the direction 
of the study of mental organization, as distinguished from 
the study of bodily structures. 

Spencer's application of psychology to sociology. Another 
illustration from a later period of human development which 
will also emphasize the significance of psychological study 
for anthropology is to be found in Spencer's discussions, in 
which he calls attention to the fact that the growth of civili- 
zation depends upon the broadening of the individual's men- 
tal horizon. He points out the fact that the savage who had 
interest in only a small range of territory and the present 
enjoyment of objects immediately about him gradually de- 
veloped into the semicivilized man interested in a larger 
territory, a larger number of individuals, and a longer period 
of time. The planting of crops and the erection of perma- 
nent buildings cannot be explained by objective conditions 
as has sometimes been attempted in the history of civiliza- 
tion. There must be ideas and imaginations in the mind of 


some active being before the future can be anticipated suffi- 
ciently to lead to the planting of the crop or the erection 
of the building. 

Relation of educational practices to scientific psychology. 
Conspicuous among the social institutions to which psychol- 
ogy may be applied in a direct and practical fashion is the 
institution of education. Here again is a type of adaptation 
which has grown in an unscientific way to a high degree of 
maturity. This statement implies no disposition to deny the 
effectiveness of many of the practices of educational institu- 
tions. They may be effective without being scientific. They 
are the outgrowth of a need which has been felt by every 
generation, and the educational institutions which have been 
developed in response to this general need have been refined 
and modified in view of experience, until finally they express 
with a high degree of perfection the final judgment of many 
generations upon important questions connected with the 
training of the younger generation. Yet there are obvious 
reasons why these historical institutions should be reexam- 
ined. Some of the uncritical methods of education are found 
to be wasteful ; again, the educational practices of different 
peoples or different sections of the same nation are found 
to be inharmonious. There arises, therefore, a demand for 
a careful analysis of the whole situation and the establish- 
ment of those practices which scientific analysis can justify. 
It is true that many hold the same attitude with regard to 
education that they do with regard to art ; namely, that it is 
safer to rely upon the intuitions of human feeling than to 
attempt to formulate an abstract system of education. Those 
who adopt this position with regard to the advantages of in- 
tuition in education have justification for their position, in 
so far as educational practices are refined to a point beyond 
our knowledge of the laws of human development. The 
most acceptable plea for a scientific study of education which 
could be presented to such persons would consist in a plea 


for a more complete knowledge of the same sort which they 
have in their native intuitions. It might be said, for exam- 
ple, that the study of educational methods involves nothing 
more than the bringing together of the individual experi- 
ences and practices of all those who have become skilled in 
educational practice. A comparative study would help to 
eliminate those individual intuitions which are incorrect, 
because they are based upon too narrow experience. 

Psychology as a preparation for the intelligent diagnosis 
of particular situations which arise in educational practice. 
The final examination of educational practices must go much 
further, however, than is implied in this appeal for a com- 
parative study of intuitions. Attention must be called to the 
fact that much of our devotion to traditional educational prac- 
tices is nothing more or less than a deliberate confession of 
our ignorance of the way in which the human mind develops. 
When a teacher is confronted by children who are unable 
to comprehend the lesson which has been set, he very com- 
monly can make no analysis of the child's difficulty. He 
then covers up his ignorance of the step which should be 
taken by requiring repeated efforts on the child's part, until 
in some unknown fashion the difficulties are mastered. It 
does not follow that the particular difficulty encountered in 
any given case would have been recognizable if the teacher 
had made a study of human development in other individ- 
uals, but the probability that the trained teacher will be able 
to make a scientific analysis of the difficult situation at hand 
is increased if he becomes acquainted with the principles 
and results of scientific psychology. Intuition should there- 
fore be supplemented by as full an account as can be given 
of the way in which mental processes go on and of the 
methods by which these processes may be examined. 

A few illustrations may serve to make clear the place 
and value of the psychological study of educational prob- 
lems. First, a number of investigations have recently been 



undertaken with a view to defining in detail the course of 
development of certain habits. Broadly stated, the conclu- 
sions of these studies show that no habit develops in all of 
its stages at a uniform rate. There is at the outset a period 
during which improvement is relatively very rapid ; this is 
followed by a period of slow development, which in turn 
gives way to successive periods of rapid and slow growth. 




, 80 

Weeks of Practice 
32 16 80. 24 28 

36 40 

Slowest Main Line Kate 

FIG. 60. Curves for sending and receiving telegraphic messages 

The curve is published by Bryan and Harter. The number of weeks of practice is 

indicated in the upper part of the figure. The number of letters which can be 

received and sent in a minute is represented in the vertical. The figure is divided 

by a horizontal line, which shows the standard rate 

A curve illustrating the process of learning. One of the 

earliest investigations of the way in which an individual 
learns may be described in detail. This investigation was 
undertaken to determine the rate at which a learner acquired 
the ability to send and receive telegraphic messages. The 
selection of this particular case for the test was due to the 
ease with which measurements of proficiency could be made 
and to the maturity of the persons investigated, which made 
it easy to subject them to a series of tests. In Fig. 60 the 


results of the investigation are represented in a curve. Along 
the top of the figure are marked the successive weeks during 
which the investigation was carried on ; along the vertical 
line at the left the number of letters which could be received 
or sent in a minute. A single point on the curve repre- 
sents, accordingly, both a stage in the practice series and 
the number of letters which could be received or sent dur- 
ing a minute at this stage of development. The curves taken 
in their entirety represent the gradual increase in the ability 
of the subject. It will be noticed, in the first place, that the 
improvement in sending and in receiving messages followed 
an entirely different course, both with reference to rate of 
improvement and also with reference to the successive stages 
of development. Concentrating attention for the moment 
upon the curve which records improvement in receiving, 
we see that the development is at first rapid and then for a 
long time practically stationary. After the stationary period, 
or plateau as the authors called this part of the figure, came 
a second rapid rise in the curve. 

Significance of a ft plateau " in development. In Fig. 61 
a second curve of the same sort is shown, which makes it 
possible to explain the pause, or plateau, in development. 
The lowest curve in this second diagram represents the 
development of proficiency in recognizing isolated letters. 
The second curve represents the development of proficiency 
in receiving isolated words which did not unite into sentences, 
and the full curve represents, as before, the development of 
efficiency in receiving words which constituted sentences. It 
will be noticed that the ability to receive isolated letters and 
the ability to receive isolated words developed rapidly for a 
time, until they reached their maxima, and then they con- 
tinued indefinitely at the same level. This level is so related 
to the plateau in the total curve that the plateau can safely 
be defined as the period during which the subject was in 
the word stage of development, rather than in the sentence 



stage. Only after the ability to receive single words had 
been thoroughly matured was a new type of development 

Other examples of the same type of development. Such 
an analysis as this of a case of learning shows much with 
regard to the psychological character of the process. It also 


Weeks of Practice 
8 J2 16 20 24 

'28 313 

Slowest Main Litee Rate 

FIG. 61. Analysis of the receiving curve 
This figure is similar to Fig. 60. For further discussion, see text (p. 339) 

suggests the possibility of including the process of mental 
development under certain broad laws of development. 
There are many analogous cases in general evolution where 
it has been noted again and again that periods of rapid 
development are followed by long periods of assimilation. 
It is a well-known fact of bodily growth that the enlarge- 
ment of the body is most marked at certain periods in the 
year and at certain well-defined periods in the child's life. 
After one of the sudden enlargements of the body, there 
follows a period of gradual assimilation of the new develop- 
ments, during which the body remains stationary in its size 


for a considerable time. The facts of organic evolution on 
a larger scale are of the same type. During certain periods 
the animal kingdom has advanced rapidly by the production 
of new forms, after which long stationary periods appear, 
during which these new forms are more completely adjusted 
to their environment without being in any important sense 
modified. Such statements as these make clear the distinc- 
tion between assimilation and acquisition in both the physical 
and mental worlds. 

The fact that certain forms of mental development are 
periodic rather than continuous is illustrated in many cases 
where quantitative tests have not been made. It has often 
been casually observed that a mature subject learns a foreign 
language, not with uniform rapidity, but in a way analogous 
to that shown in the curves given above. At first there is 
rapid acquisition of the words and grammatical constructions 
of the new language, but after a time the power to acquire 
new phases of the language seems to be brought to a stand- 
still, and the period of discouragement which follows is 
often felt by the learner to be a period of no development, 
while in reality it is a period of assimilation and preparation 
for the later stages of growth. When the later development 
into the full use of the language comes, it is so sudden and 
striking in its character that it has been noted time and time 
again as a period of astonishing mental achievement. 

Motor habits intermittent. Many habits of action exhibit 
the same type of intermittent development. If one learns 
some manual art, he finds that the ^coordinations with 
which he begins are only gradually eliminated ; but finally he 
learns the combination which is advantageous, and from that 
point on the improvement seems for a time to be very rapid. 
It is sometimes advantageous in a course of training to give 
up practice for a time in order that the various elements of 
the coordination may have an opportunity to readjust them- 
selves and in order that the new efforts at development may 


begin at a new level. Professor James has made the striking 
remark that we learn to skate during the summer and to swim 
during the winter. The significance of this observation is 
that it recognizes the intermittent character of the develop- 
ment of habit and the advantage of a period of assimilation, 
sometimes even of a period of complete cessation of the 
activity in question. 

School training in its relation to the stage of development 
attained by the mind. From the point of view of practical 
education, it is obvious that the types of training which 
should be given at the different periods in mental develop- 
ment are by no means the same. During a period of rapid 
acquirement of new material, one sort of training is appro- 
priate ; during a period of delayed assimilation, that form 
of training is most appropriate which is technically known 
in the schools as drill. The ordinary unscientific education 
has recognized vaguely that there is a difference in the 
kinds of training demanded at different times ; but the ad- 
justment of these different types of training to the demands 
of individual mental development is an intricate problem 
which can be worked out satisfactorily only when a careful 
study is made of educational practice. 

Significance of scientific studies often indirect. The value 
of scientific studies of habits and of forms of training is 
shown by such considerations as the foregoing. It also 
becomes evident that such studies do not necessarily change 
the subjects of instruction nor even the general methods 
established by tradition, but serve rather to refine our knowl- 
edge of the process of mental growth and make it possible 
for us to deal with different stages of the educational process 
with much greater precision. To justify scientific investiga- 
tions which seem at first sight remote from school problems, 
it may be well to point out that the solution of one problem 
in mental development makes it possible to attack all other 
problems of a similar kind more intelligently. If one knows 


with scientific precision that a period of assimilation occurs 
in one case of mental development, he will be better pre- 
pared to discover and understand a similar period in other 
cases where it may be less easy to make an exact scientific 
study. For example, we get useful suggestions to guide us 
in understanding children's reading from the study reported 
above on learning telegraphy. The mastery of the word ele- 
ments in ordinary reading is similar to the mastery of these 
same elements in the case of the telegrapher. 

Expression as an essential condition of mental life. An- 
other concrete illustration of educational progress may be 
found in the fact that there is a general disposition among 
educators to-day to recognize the importance and value of 
expressive activities in all educational processes. The early 
type of education was that in which sensation processes were 
emphasized almost to the exclusion of activities. Whether 
the educational practice which emphasized impressions can 
be attributed to the sensation psychology which was contem- 
porary with it, or whether the sensation psychology was the 
outgrowth of a false educational theory, is a question which 
need not be discussed here. Certain it is that the limited 
view of mental life and the false principle of education, both 
of which emphasized impressions rather than expression, 
existed for a long period side by side. It may have been 
the growing experience of practical teachers which led to 
the discovery of the fallacy in the doctrine that mind is 
conditioned primarily by impressions. It may have been 
the insight of scientific students which gradually made it 
clear that human activity must always be recognized in dis- 
cussing the processes of mental development ; or it may be 
that the two lines of thought and practice grew up together. 
In any case, it is certain that a transformation of educational 
practice and a corresponding transformation of psychology 
have been going on for a generation, until now we have 
in both an emphasis on bodily activities. 


Psychology historically a part of philosophy* Turning 
from these practical applications of psycholg^ro education, 
it remains for us to discuss one of the applications of psy- 
chology which has always been recognized in the historical 
development of this science ; namely, the relation of psy- 
chology to the philosophical disciplines. Indeed, it may be 
said that psychology was not only applied to the problems 
of philosophy ; it was originally devoted to the discussion of 
these problems to such an extent that it was regarded as an 
integral part of philosophy, not as an independent science. 
Philosophy deals with the ultimate nature of matter and 
mind, with the fundamental laws of reality and the relation 
of reality to human experience, with the ultimate nature of 
truth, goodness, and beauty. There have been times, for 
example during the medieval period, when the interest in 
such ultimate problems ran so high that there was little or 
no attention given to the special problems of science. The 
time came, however, with the development of modern 
thought when these larger problems receded into the back- 
ground and men began to concern themselves with the 
phenomena in the world rather than with the ultimate reali- 
ties underlying these phenomena. It is characteristic of the 
present scientific period that the special sciences neglect 
to as great an extent as possible the questions of ultimate 
reality. The student of psychology participates to a very 
large extent in this tendency to omit from his discussion 
questions relating to the ultimate nature of mind, lie 
cannot, however, accept as final this aloofness from the 
broader questions, for he finds himself, more than his 
neighbor who deals exclusively with the natural sciences, 
led to ultimate problems. 

Relation of psychology to philosophy closer than that of 
any of the special sciences. When, for example, one points 
out that a sensation is related to a fact of external energy 
indirectly through the organs of sense, or when one points 


out that space is a definite form of perception on the one 
hand, and of arrangement of objects on the other, the 
psychologist is driven to consider the relation between con- 
sciousness and the external world more than the student of 
the other particular sciences. The student of natural science 
uses in every act of observation the relation between subjec- 
tive experience and the physical world ; he exercises his 
mind in trying to know the world, but his interests are 
always centered on the relations between things, never on 
the relation between things and consciousness. Hence the 
student of natural science easily avoids questions relating 
to the ultimate interaction between himself and the physical 
world. The student of psychology cannot escape these 
questions. 1 1 is study of sensation pushes him in the direc- 
tion of an examination of this relation. Furthermore, when 
the student of psychology finds that the construction of 
concepts is an elaborate mental activity, he is immediately 
led to ask not only what are the laws which control such 
conceptual activity, but also what are the relations of scien- 
tific ideas to external reality, and what are the laws which 
determine the validity or lack of validity of these concepts. 
It is true that psychology cannot answer all of these ques- 
tions, and it has been our purpose in the foregoing discus- 
sions to adhere as closely as possible to the sphere of strict 
psychological inquiry, postponing these ultimate questions 
or entirely omitting them. It is, therefore, very appropriate 
that we should call attention at the end of our inquiry to 
the disciplines which deal with these more elaborate inquiries, 
and that we should define their relation to psychology. 

Psychology and logic. Logic attempts to formulate the 
laws of valid reasoning. To be sure, logical principles can 
be worked out without the aid of psychology, through 
repeated efforts to reason correctly, but the clear definition 
of logical relations waits on the psychological descriptions 
of the mental processes involved in reasoning. 


Psychology and aesthetics. The second branch of phi- 
losophy is aesthetics. In earlier chapters reference has 
been made repeatedly to the underlying principles which 
control the recognition of symmetry and regularity of form, 
and it was pointed out in earlier paragraphs of this chapter 
that the canons of architecture and painting are directly re- 
lated to certain fundamental principles of human feeling and 
recognition. There still remain a large number of special 
analyses and special considerations which must be worked 
out in order to define fully the canons of taste in each field 
of art and the general canons of taste which underlie all 
forms of art. Such considerations of the canons of art 
constitute a legitimate development of the general psycho- 
logical studies which have been suggested, and constitute 
the special discipline of aesthetics. 

Psychology and ethics. When we turn to the third of 
the special philosophical disciplines, namely ethics, we find 
again a natural relation to psychology, though it is perhaps 
proper to emphasize here more than in the case of logic or 
aesthetics the independence of ethical canons from purely 
subjective organizations. The Tightness or wrongness of 
human behavior is not understood primarily through an 
analysis of the processes of behavior themselves. The 
Tightness or wrongness of behavior depends upon certain 
broad considerations involving the social interrelationships 
of the active individual. It is necessary, therefore, to make 
a study of the extra-mental or social relations of the indi- 
vidual in order to establish the canons of ethical conduct. 
One does not need to discuss the extra-mental relations to 
anything like the same extent when he attempts to define 
the laws of reasoning in logic or the laws of appreciation 
in aesthetics. It is true that the individual's modes of be- 
havior, as they have been worked out in the course of 
social life, come to embody much of the social interrelation- 
ship which determines their ethical validity. The individual 


who has grown up in a social group ultimately conforms 
in his modes of thought and internal organization to those 
social demands which are imposed upon him by the com- 
munity in which he lives. It is probably true, therefore, 
that in the last analysis the fundamental truths of ethics 
are expressed in the internal organization of the individual 
as well as in the forms which are approved under the 
canons of social life, but the development of ethical laws 
lies somewhat beyond the application of psychology. We 
come to ethics chiefly through the study of the applications 
of psychology to the sciences of social institutions. 

Psychology and metaphysics. When we turn from the 
special philosophical disciplines to the broader field of meta- 
physics, or the general theory of reality, we find that the 
relation of psychology to these broader types of considera- 
tion is relatively indirect. Metaphysics takes up the results 
of natural science which deals with matter and of psycho- 
logical science which deals with consciousness, and attempts 
to formulate some general principles of the relations between 
all forms of reality. To this general discussion psychology 
cannot contribute final answers any more than could the 
special sciences of physics or chemistry. Psychology can 
only present its conclusions after it has carried out as com- 
plete an analysis of consciousness as possible, and must 
leave it for metaphysics to make an ultimate comparison of 
these facts with the physical facts. The student who finds 
that an empirical analysis of consciousness conflicts with 
any of the established views which constitute a part of his 
general theory of the world should recognize that it is not 
the function of any single science to reconstruct his total 
theory of the world. He will have to accept the results of 
empirical analysis in all the different spheres of exact 
research and work out a general view which will include all 
of these results. The conclusions of psychology need to be 
generalized exactly as do the conclusions of physics and 


chemistry. No generalization will be finally valid which 
does not comprehend the empirical analysis of each one of 
these sciences. Furthermore, it should not be forgotten 
that there are many types of consideration which forced 
themselves upon human attention long before the various 
forms of scientific analysis could be worked out, and these 
considerations must also be recognized in the construction 
of a broad philosophy of life. The generalizations which 
were reached before the development of the special sciences 
require revision in order to include the results of these 
sciences. This fact should not disturb the mind of any 
student and need not lead him to ignore many nonscientific 
types of experience. The training in scientific inference 
which he has received in the study of empirical psychology 
should lead him to recognize that all generalizations are 
subjective constructs built up from a great variety of experi- 
ences, many of which are superficially in disagreement with 
each other. The subjective construct is not to be discarded 
as invalid, because it changes with the acquisition of new 
knowledge ; one's theory of the world must change in order 
to fulfill its function as a complete, organized expression of 
the manifold experiences which enter into life. Psychology, 
more than any other science, should lead to a recognition 
of this demand for a constantly progressing enlargement of 
philosophic view. While, therefore, modern psychology as a 
science has freed itself from the obligation of dealing with 
the broad philosophical questions, it continues, when rightly 
understood, not only to contribute material for philosophic 
thought, but also to urge the student to the rational recon- 
struction of his general abstract views. It is therefore intro- 
ductory, not merely to the special philosophical disciplines 
but also to the more remote discussions of metaphysics itself. 


Abnormals, psychology of, 1 1 
Abstract words, 236 
Abstraction, 232, 263 
Accommodation, 86 
Achromatic sensations, 74 
Action, voluntary, 301 

an4 words, 235 
Active organs, glands as, 138 

muscles as, 134 
Adaptation, conscious, 4 

human, and ideas, 251 
Aerial perspective, 184 
Esthetics, 346 

After-effects of hypnosis, 295 
After-images, auditory, 114 

table of, i oo 

visual, 94 

Agreement, internal, as test of im- 
agination, 257 
Alcohol, 285 

Alligator, nervous system of, 31 
Alphabet, blind, 167 

evolution of, 222 
Altruism, 151 

American Crowbar Case, 58 
Amplitude, 78 

of vibrations, 78 
Anaesthesia in hypnosis, 290 
Analysis, perceptual, 316 

scientific, of consciousness, 65 
Analytical psychology, v 
Anger, 152 
Angier, R. P., vii 
Animal language, 212 
Animal psychology, 10 
Animals, unicellular, 15 
Anthropology and psychology, 333 
Aphasia, 56 

Apparatus in experiments, 8 
Application and verbalism, 323 
Applications of psychology, 69, 325 
Aqueous humor, 85 
Arabic numerals, 229 
Architectural harmony, 327 

Arithmetic, development of, 229 
Armstrong, A. C., vi 
Art, 325 

freedom in, 326 
Articulation, selection of, 214 
Association, 245 

principle of, 59 
Association area, Broca's, 57 
Association areas, in cortex, 50, 

52, S3 

frontal, 58 

in human cerebrum, 54 
Association centers, 29 
Atom, concept of, 262 
Attention, 62, 156, 160 

and gesture, 216 

involuntary, 303 

voluntary, 301 
Attitudes, 66, 69, 142, 233 

control of, 319 

external, 155 

fundamental, 146 

ideational, 254 

mental, 207 

Auditory area in cerebrum, 52, 53, 54 
Auditory organ, 109 
Auditory sensations, 100 
Auditory sensory processes, 1 1 1 
Auditory space, 169 
Axis cylinder, 39 
Axone, 39 

Barter, 252 

Basilar membrane, 109 
Beats, auditory, 112 
Behavior, $ 
animal, 248 

and attitudes, 142 

and belief, 266 

and consciousness, 17 

and education, 343 

and experience, 130 

fundamental forms of, 23 

of higher animals, 34 




Behavior, higher forms of, 34, 68, 


higher types of, and ideas, 304 

ideational, 248 

and imagination, 256 

individual, 136 

inherited, 138 

and instincts, 199 

of multicellular animals, 22 

nerve cells, 41 

and organization, 313 

organization of, 140 

scientific studies of, 309 

selective consciousness, 132 

and sensitivity, 17 

simplest types of, 16 

speech, a form of, 209, 217 

of unicellular animals, 16 

voluntary, 301 

and words, 235 
Behaviorism, iii 
Belief, 265 
Berkeley, 179 
Binocular vision, 180 
Biological evolution, 334 
Biology and psychology, 3 
Blind spot, 9 

Blind, the, tactual percepts of, 167 
Brightness, 77 
Broca, 56 
Bryan, 338, 340 

Cajal, 41, 44, 45, 49 
Cameron, E. H., vii 
Canals, semicircular, 107 
Cause, idea of, and self, 275 
Cells, gustatory, 120, 121 

muscle, 134 

nerve, 39 

olfactory, 117, 118 
Centers, in cerebrum, 50, 52, 53 

higher, 29 

nervous, 29 
Central nerve cells, 22 
Central nervous system, 25 
Cerebellum, 28, 45 

evolution of, 31 

human, 38 

Cerebral processes and choice, 305 
Cerebrum, 28 

cortex of, 50 

evolution of, 31 

human, 38, 47 

Chemical senses, 123 
Child psychology, 10 
Child's idea of self, 270 
Child's imagination, 259 
Chinese writing, 221 
Choice, simple, 304 

voluntary, 68 

Choroid coat of eye, 85, 87 
Chromatic sensations, 74 
Circulatory activities, 1 54 
Circulatory movements, 154 
Classification, of conscious proc- 
esses, 61 

threefold, 63 
Cochlea, auditory, 108 
Codfish, nervous system of, 31 
Coherency, criterion of, 258 
Cold spots, 122 
Color, 74 
Color blindness, 90 

of periphery of retina, 89 

table of, 99 
Color circle, 76 
Color-mixing, 92 

table of, 100 
Color names, 75 
Colors, complementary, 93 
Combinations of sensations, 163 
Communication, animal, 213 

systems of, 212 
Complementary colors, 93 
Concept of self, 269, 272 
Concepts, 251 

scientific, 262 

validity of, 263 
Concrete words, 235 
Conduct, control of, 253 
Cones of retina, 87, 88 
Conflict of instincts, 200 
Conn, 83 
Consciousness, and behavior, 17 

definition of, 12 

and evolution, 3, 250 

and heredity, 203 

nervous conditions of, 5 

and nervous structures, 38 

and physical facts, 72 

selective, 130 

and sympathy, 160 
Content, literary, 329 
Contiguity, association by, 245 
Contractile cells, 19 
Contractility, 15 



Contrast, association by, 246 

of self and not-self, 271 

space, 174 

visual, 96 

visual, table of, 100 
Control, of behavior, 135 

in mental hygiene, 315 
Coordinating center, nervous sys- 
tem as, 25 
Coordination, 136 

of activities, 314 
Cord, human, 38, 42, 44 

spinal, 28 
Cornea of eye, 87 
Cortex, of cerebellum, 45 

cerebral, 44, 49, 50 
Corti, arch of, 1 10 
Creation theory of language, 210 
Criticism, of ideas in hypnotism, 

of imagination, 256 

literary, 260 
Crowbar Case, 58 
Current, nervous, 21 
Czermak, 104 

Darwin, 202 

Deafness, tone, 115 

Decision, 306 

Definition of psychology, 12 

Delayed instincts, 198 

Delirium, 287 

Dendrites, 39 

Depth, visual, 179, 186 

Design in art, 324 

Development, plateau in, 339 

of self-consciousness, 269 

of space, 1 65 

Diagnosis, psychological, 337 
Difference tones, 112 
Differences, individual, 2 
Diffusion, 203, 204, 206 

nervous, 60 
Digestion, 15 

in higher forms, 19 
Direct behavior, 248 
Disappointment, 155 
Discord, 114 

Discrimination and words, 227 
Diseases, toxic effects of, 286 
Displeasure, 147 
Dissociation, 278 

degrees of, 281 

Distance, of sounds, 171 

visual, 178 

Dog, nervous system of, 31 
Dove, nervous system of, 31 
Dreams, 283 
Drugs, 279, 285 
Dual personality, 292 

in hypnosis, 291 

Ear, evolution of, 103 

structure of, 104 
Ebbinghaus, 113 
Economy of mental effort, 320 
Edinger, 46, 47, 48 
Education, 336 

and choice, 309 
Efficient cause and self, 275 
Elements of consciousness, 73 
Embryological methods of localiza- 
tion, 53 
Emotional expression and speech, 


Emotional life, disturbance of, 299 
Emotional reactions, 253 
Emotions, 147 

in experiments, 8 

higher experiences, 153 
Empirical tests of imagination, 257 
Equilibration, organ of, 107 
" Essay toward a New Theory of 

Vision," 180 
Ether, concept of, 258 
Ethics, 346 
Eustachian tube, 106 
Evolution, and behavior, 133 

of belief, 265 

of complex organisms, 32 

and consciousness, 3, 250 

of ear, 103 

of eye, 80 

of gestures, 217 

human, 333 

of ideas, 253 

of instincts, 198 

of muscles, 134 

of nervous system, 31 

parallel of behavior and structure, 


Excessive excitation, 298 
Excitation, process of, 21 
Experience, and behavior, 130 

definition of, 12 

and emotions, 152 



Experience, of lower animals, 27 

ordinary, i 

and physical facts, 2 

and time, 191 

Experiences, classifications of, 63 
Experiment, auditory space, 170 

in psychology, 7 
Experimental psychology, 11 
Experiments, on the present, 191 

reaction, 310 

Expression and mental life, 343 
Extensor movements, 1 54 
Extirpation, 51 

as method of localization, 51 
Eye, evolution of, 80 

human, 84 

Facilitation, principle of, 59 

Familiarity, visual perception, 184 

Fatigue, 280 

Fatigued nerve cells, 280 

Fear, 148, 149, 150, 201 

Fechner, 129 

Feeling, 63 

and intuition, 329 

organic, 153 

Feelings, cultivated, 147 
Fibers, in cerebrum, 47 

nerve, 39 

systems of, in cerebrum, 47 
Figures : 

Association fibers, 47 

Association by similarity, 245 

Balance, 158 

Binocular parallax, 182 

Blind spot, 9 

Cerebellum, human, 45 

Cerebral centers, 52, 53 

Cerebral cortex, 49, 50 

Cerebrum, human, 46 

Chinese writing, 221 

Cochlea, auditory, 109 

Color circle, 76 

Cord, human, 44 

Corpus callosum, 48 

Curve of sleep, 282 

Development of telegraphic lan- 
guage, 338, 340 

Ear, 104 

Evolution of eye, 82 

Evolution of letter M, 222 

Eye, human, 85 

Fatigued nerve cells, 280 

Human nervous system, 38 
Involuntary movements during 

attention, 157 

Localization of functions, 52, 53 
Movements of unicellular ani- 
mals, 1 6 

Muller-Lyer illusion, 172 
Muscle cell, 134 
Muscle cells, primitive, 20 
Muscular contraction, 135 
Nasal cavity, 116 
Nerve cells, 20, 39, 40 
Nerve cells, evolution of, 41 
Nervous system of alligator, 31 
Nervous system of codfish, 31 
Nervous system of dog, 31 
Nervous system of dove, 31 
* Nervous system of frog, 28 
Ojibwa love letter, 220 
Olfactory cells, 117, 118 
Peduncular fibers, 46 
Photographs of eye movements, 


Poggendorff illusion, 176 
Relation of retinal image to size 

of object, 179 
Retina, 88 
Sensory cells in vestibule of ear, 

Sensory processes and reactions, 


Sound waves in beats, 113 
Space-contrast illusion, 174 
Spinal cord, human, 42, 44 
Stag beetle, nervous system of, 25 
Starfish and nervous system, 24 
Structure of hydra, 18 
Synapses, 40 
Taste bulbs, 119, 120, 121 
Touch organs, 124, 125, 126, 127 
Wave forms, 77 
/Collner illusion, 176 

Figures of speech, 238 

Fiske, John, 151, 152 

Flechsig, 52 

Flexor movements, 154 

Food instincts, 198 

Form, recognition of, 132 

Fovea cent ml is ^ 89 

Franklin, Mrs. C. L., 97 

Freedom of will, 308 

Frog, behavior of, 35 
nervous system of, 28 



Fusion, 64, 67, 70 
of sensations, 163 
and space, 187 
and use, 190 

Galton, 242 

General ideas and words, 234 

Generalization, 264. 

Geometrical perspective, 184 

Gesture language, 216 

Glands, active organs, 138 

Golgi-Mazzoni corpuscle, 125 

Gossip, evolution of word, 231 

Gravity, concept of, 232 

Gray, sensations of, 74 

Gray matter, nervous, 42 

GreefT, 88 

Greek column, 158 

Greek philosophy and psychology, 2 

Habit, 304 

and consciousness, 207 

and diffusion, 203 

and instinct, 202 

and perception, 191 
Habits, 195 

derived from instincts, 199 

motor, 341 

I lair, nerves around, 126 
llaller, 18, 20 
Hallucinations, 278 
Handwriting, habit of, 204 
Harmony, musical, 114 
Harter, 338, 340 
Heat spots, 123 
Hebrew alphabet, 223 
Ilelmholtz, no, in 
Herrick, 108, 109 
Higher animals, behavior of, 34 
Hodge, 280 
Hydra, 18 

Hygiene, mental, 314 
Hyperaesthesia in hypnosis, 290 
Hypnosis, 279, 287, 288 

Idea of self, 269 
Ideas, 70 

abstract, 263 

balancing of, 306 

characteristic of man, 239 

dominant, 321 

in dreams, 283 

flexibility of, 247 

general, 264 

higher behavior, 304 

and higher social life, 268 

and impressions, 240, 241, 254 

influence of, 249 

and memory, 240 

scientific, 258 

and speech, 209, 215 

verbal, 233 
Ideation, 68 

wholesome, 320 
Ideational attitudes, 254 
Ideational behavior, 248 
Illusion of weights, 159 
Illusions, 278 

optical, 172 
Imageless ideas, 232 
Imageless thought, 246 
Imagery, and ideas, 246 

individual variations in, 242 

and words, 232, 233 
Images, and ideas, 237 

memory, 6 

as obstructions to thought, 238 
Imagination, 251, 254 

child's, 259 

literary, 260, 330 

personifying, 255 

uncritical, 259 
Imitation, and speech, 212 

theory of speech, 210 
Impressions, and ideas, 254 

not ideas, 240 

sensory, 66 
Impulse, 302 
Incus, 106 

Indirect behavior, 219, 248 
Indirect nervous centers, 30 
Individual, higher, self-sufficiency 

of, 33 

Infant expression, 214 
Infant recognition of space, 165 
Inheritance of nervous structures, 


Insanity, 279, 294, 296 
Instinctive behavior, 301 
Instinctive life, disturbance of, 299 
Instincts, 26, 138, 196, 198, 207 

and religion, 267 

and sentiments, 267 
Intensities, sensation, 126 
Intensity of sounds, 102 
Interest and behavior 132 



Interjection theory of speech, 211 
Intervening objects and visual 

space, 185 
Intoxication, 286 
Introspection, 4, 13, 14, 311 

and classification, 66 

defects of, 6 

sensations, 141 

Introspective psychology, 331 
Intuition and feeling, 329 
Involuntary attention, 303 
Irritability, 15 
Irritable cells in higher forms, 19 

James, William, vi, 342 
Jastrow, 157 
Jealousy, 152 
Jennings, 16 
Judgment, 264 

Kipling, 149, 150, 151 
Knowledge, 63 
Kohlschutter, 282 

Language, 209 

and ideas, 215, 322 
Law, Weber's, 127 
Learning curve, 338, 340 
Learning handwriting, 205 
Learning, units of, 320 
Lens, evolution of, 83 

of eye, 85 

Letters, evolution of, 222 
Libertarianism, 308 
Life, concept of, 275 
Light, analysis of, 3 

external, 78 
Literary content, 329 
Literary imagination, 260 
Local signs, 168 

Localization of brain functions, 50, 58 
Location, auditory, 169 
Locke, John, I 
Locomotion, instinct of, 199 
Loeb, 24 
Logic, 265, 345 
Lotze, 1 68 

Loudness of sounds, 102 
Love, parental, 151 

M, letter, evolution of, 222 
Mallery, 220 
Malleus, 105 

Meatus, external, 104 

internal, 106 

Mechanical laws and space, 187 
Mechanical senses, 123 
Medulla, 28 

human, 38 
Melancholia, 297 
Memory, 14, 64, 67, 70, 196, 320 

experiments in, 7 

and ideas, 240 

physiological conditions of, 32 

training of, 243 

and words, 226 
Mental hygiene, 314 
Metaphysics, 347 
Method, indirect, in psychology, 14 

in psychology, 4 
Methods of brain localization, 50 
Mind and evolution, 333 
Missenian corpuscle, 124 
Mixed colors, 77 
Motive for psychology, i, 2 
Motor area, cerebral, 55 
Motor areas in cerebral cortex, 50, 


Motor nervous process, 22 
Motor processes, 59, 64 

in sleep, 284 
Motor reactions, 311 
Movements, analysis of, 311 

and attitudes, 154 

eye, 175* 176 

in reactions, 312 

undeveloped, 206 

and visual perception, 186 
Miiller-Lyer illusion, 172 
Multicellular animals, 18 
Multiple personality, 293 
Muscle cell, 134 
Muscle, sense organs in, 125 
Muscles of eye, 84 
Muscular tension, general, 302 
Mythology, 259 

Nagel, 52 
Narcotics, 285 
Nasal cavity, 116 
Negative after-images, 95 
Nerve cells, 39 

evolution of, 41 

fatigued, 280 

types of, 22 
Nervous centers, higher, 31 



Nervous conditions, of conscious- 
ness, 5 

and drugs, 285 
Nervous current, 21 
Nervous processes and sensations, 7 2 
Nervous structures and conscious- 
ness, 38 

Nervous system, as basis of psycho- 
logical classification, 61 

and behavior, 35 

centralized, 23 

of frog, 28 

human, 38 

stag beetle, 25 

starfish, 24 

1 vertebrate, 27 et seq. 
Neurones, 39 

evolution and development of, 41 
Newton, Isaac, 3 
Noise, 1 02 
Number names, 228 
Number terminology, 227 
Numerals, systems of, 229 

Objective, 13, 271 

Objects and perception, 188 

Observation, and classification, 61 

in psychology, 8 

self-, 4 

Occult in psychology, 2 
Ojibwa writing, 220 
Olfactory lobes, 28 
Olfactory organ, 116 
Optic lobes, 28 
Optical illusions, 172 
Organ of Corti, 109, 1 10, 1 1 1 
Organic activities, 315 
Organic feelings, 1 53 
Organic retentiveness, 195 
Organic sensations, 125 
Organization, 64 

for behavior, 34 

of behavior, 141 

concept of, in psychology, 313 

and decision, 306 

and diffusion, 60 

idea of, 275 

of ideas, 254 

normal consciousness, 287 

principle of, 60 

self-directed, 324 

and thought, 320 
Ossicles, chain of, 106 

Overexcitation, 286 
Overtones, 102 

Facinian corpuscles, 124 
Pain, 62 
Pain spots, 123 
Parental love, 151 
Paths, nervous, 26 

nervous, in cord, 42 
Peduncular fibers, 46 
Perception, 67, 164, 174, 304 

of objects, 1 88 

summary of, 194 
Percepts, of blind, 167 

and habits, 191 

and repetition, 190 
Perceptual analysis, 316 
Perceptual behavior, 248 
Perceptual process, example of, 252 
Perceptual synthesis, 317 
Personality, disorganized, 278 

dual, 292 

dual, in hypnosis, 291 

multiple, 293 

scientific idea of, 274 

and volition, 308 
Personifying imagination, 255 
Perspective, aerial, 184 

geometrical, 184 
Philosophy, 344 

Photographic records of eye move- 
ments, 175 
Phrenology, 57 
Physical facts, and consciousness, 


and experience, 2 

Physiological conditions, of con- 
scious processes, 249 

of experience, 14 

of habit, 201 

of sleep, 279 

Physiological psychology, v, 1 1 
Physiology, visual perception, 175 
Pictographic writing, 219 
Pigment-mixing, 94 
Pinna of ear, 103 
Pitch, 10 1 

Plateau in learning, 339 
Play, 137 
Pleasure, 62, 146 
Poggendorff, 176 
Positive after-images, 95 
Post-hypnotic effects, 295 



Practice, effects on illusions, 173 

and illusions, 177 
Preface, first edition, v 

second edition, iii 
Present, the, 191 
Pressure spots, 123 
Prevision, 307 
Primary colors, 75 
Problem, meaning of term, 237 
Protective instincts, 197 
Protoplasm, 15 
Psychiatry, n, 299 
Psychology, abnormal, 278 

and aesthetics, 346 

animal, 10 

and its applications, 268, 325 

and biology, 3 

child, 10 

definition of, 12 

and ethics, 346 

experimental, 8, 1 1 

forms of, 10, ii 

functional, v 

Greek, 2 

and logic, 345 

and metaphysics, 347 

and philosophy, 344 

and physics, 3 

physiological, v, 5, n 

scope of, 12, 69, 70 

social, ii 

structural, v 

subdivisions of, 10 
Psycho-physics, 73 
Purple, 76 
Purpose and choice, 309 

Quality, tonal, 101 

Reaction experiments, 310 
Reaction times, 310 
Reactions, 66 

motor, 311 

sensory, 311 
Reading of blind, 167 
Reasoning, 264 
Rebus and alphabet, 223 
Recall and memory, 244 
Recency and memory, 243 
Recognition and attention, 161 
Reflex, 44 

Relativity of temperature sense, 123 
Religion and self-consciousness, 273 

Religious belief, 267 
Reproduction, 15 

evolution of, 33 

in higher forms, 19 
Retention and memory, 244 
Retentiveness, organic, 195 
Retina, 87 

Retinal image, size of, 178 
Retinal rivalry, 183 
Retzius, 126, 127 
Rhythm, prose, 327 

and time, 193 
Rivalry, retinal, 183 
Rods of retina, 87, 88 
Rolando, fissure of, 53 
Roman numerals, 229 
Rufnni, 125 

Saturation, color, 77 
Scala, tympani, 109 

vestibuli, 109 

Science, development of, 261 
Scientific ideas, 258 
Scientific studies of learning, 342 
Self, idea of, 269 

as scientific concept, 272 

unity of, 275 
Self-consciousness, 273 

development of, 269 
Self-directed organization, 324 
Self-observation, 4, 13 
Semicircular canals, 107 
Sensation intensities, 126 
Sensations, 66, 69, 71 

auditory, 101 

combination and arrangement of, 

introspective, 141 

muscle, 125 

organic, 125 

of smell, 117 

of taste, 119 

of touch, 121 

visual, 74 
Sense organ and visual sensations, 

Senses, chemical and mechanical, 


Sensitive cells, 19 
Sensitivity, 17 
Sensory area, cerebral, 55 
Sensory areas in cerebral cortex, 
5> 5 2 53 



Sensory cells, 20 
Sensory centers, 29 
Sensory impressions, 34 

meaning of, 139 
Sensory nervous centers, 29 
Sensory processes, 22, 64 
Sensory reactions, 311 
Sentiments, 267 
Shadows, 185 
Shame, 152 

Sheath of Schwann, 39 
Signs, local, 168 
Similarity, association by, 245 
Size, perception of, 175 

visual, 178 
Sleep, 279, 281 

curve, 282 

and motor processes, 284 
Smell, 116 

rudimentary sense, 118 
Smith, C. II., vii 

Social consciousness and self, 272 
Social influence and thought of in- 
dividual, 225 

Social life arid higher mental proc- 
esses, 267 

Social motives and language, 223 
Social psychology, n 
Social sciences, 208, 331 
Sociology, 335 
Solidity, visual, 181 
Sound, localization of, 171 

physical, 101 

Sounds and communication, 213 
Space, auditory, 169 

many senses, 169 

and movement, 187 

product of fusion, 163 

tactual, 164 

visual, 172 
Specialization, 318 

of functions, 18 
Spectrum, 76 
Speech, 209 

and ideas, 215 

origin of, 210 

Speech center in cerebrum, 56 
Speech centers, 54 
Spencer, 335 
Spinal cord, frog's, 28 
Stapes, 1 06 

Starfish, nervous system of, 24 
Stereoscope, 181 

Stimulation, 21 

as method of localization, 51 
Stimuli, gustatory, 121 

olfactory, 118 
Stimulus, 20 

physical, 127 
Structural psychology, v 
Subdivisions of psychology, 10 
Subjective, 13, 271 
Suggestions, 289, 291 
Summation tones, 113 
Sylvian fissure, 54 
Symbolic value, 252 
Symbols, number, 228 

writing, 221 
Sympathy, 158 

and consciousness, 160 
Synapses, 40,41 

in sleep, 280 
Synthesis, perceptual, 317 

Tables : 

After-images, 100 

Auditory processes, 115 

Color blindness, 99 

Color contrasts, 100 

Color-mixing, 100 

Experiences, 37 

Forms of behavior, 36, 37 

Nervous structures, 36, 37 

Physical light and sensations, 79 

Red-green color blindness, 91 
Tallies, 228 

and number, 228 
Taste, sensations of, 116, 119 
Taste bulbs, 119 
Taylor, I., 222 
Telegraphic language, 338 
Temperature, production of, in ani- 
mals, 32 

Temperature spots, 122 
Tension, constant, in muscles, 


experiments on, 156 
Tensor tympani, 105 
Tests of imagination, 256 
Testute, 39, 124 
Theories, of color vision, 97 

of origin of language, 211 
Thought relations, 234 
Timbre, 102 
Time, 191 
Tone deafness, 115- 



Tones, difference, 112 

summation, 113 
Tool-consciousness, 249 
Tooth, nerve in, 127 
Touch, inner, 168 

organs of, 122 

sensations, 121 

space, 164 

Toxic substances, 286 
Tracts, nervous, 59 
Trench, 230 
Tschermak, 52 
Tympanic membrane, 105 

Uncritical imagination in dreams, 284 
Unicellular animals, 1 5 

behavior of, 16 
Unity, concept of, 276 

of objects, 189 

of self, 275 

Value, ideas of, 252 
Verbalism, 266, 322 
Verse, 328 

and time, 192 
Vesicle, auditory, 103 
Vestibule, auditory, 107 
Vibrations, light, 78 

sound, 101 
Vision, adaptation of, to behavior, 1 32 

and touch, 166 

Visual area in cerebrum, 52, 53, 54 
Visual space, 172 
Visualizers, 242 
Vitreous humor, 85 
Vividness, 62 

and memory, 243 
Volition, 63, 70, 301 

and attitudes, 319 
Voluntary choice, 68 

Walking as instinct, 199 
Wave forms, 77 
Weber, 127, 164 
Weber's Law, 127 

interpretations of, 128 
White, sensations of, 74 
Will, 63 

freedom of, 308 

Wonder, motive for psychology, I 
Words, abstract, 236 

evolution of, 230 

experiments, 226 

and general ideas, 234 

interpretation of, 6 

recognition of, 318 

social values of, 224 
Work song and language, 218 
Writing, evolution of, 219 
Wundt, Wilhelm, vi, 167 

Zollner, 176